Merge branch 'fix/install-ddd.h' into 'master'

ref:staging/dune-uggrid Fixes [#50]

See merge request [!147]

  [#50]: gitlab.dune-project.org/NoneNone/issues/50
  [!147]: gitlab.dune-project.org/staging/dune-uggrid/merge_requests/147


Closes #50

Merge branch 'feature/bump-to-2.8' into 'master'

See merge request [!146]

  [!146]: Nonestaging/dune-uggrid/merge_requests/146

Merge branch 'remove-obsolete-amglevel-access' into 'master'

ref:staging/dune-uggrid The UG3 multigrid data structure used to have an array
'amggrids' with grid levels for AMG. That array is long gone, but it was still
overwritten with nullptrs in the multigrid setup code. A serious memory bug,
and I am amazed that nobody ever observed any effects.

See merge request [!145]

  [!145]: gitlab.dune-project.org/staging/dune-uggrid/merge_requests/145

The UG3 multigrid data structure used to have an array 'amggrids'
with grid levels for AMG.  That array is long gone, but it was
still overwritten with nullptrs in the multigrid setup code.
A serious memory bug, and I am amazed that nobody ever observed
any effects.

Merge branch 'feaure/dont-use-ug-symlinks' into 'master'

ref:staging/dune-uggrid The hack to have every sub-directory in the include
path does no longer work for me. Time to get it fixed by making the include
paths relative to dune-uggrid root directory.

-   include paths relative to dune-uggrid root directory
-   move header files below dune/uggrid/.
-   drop folder ug/ and compatibility with UG 3.13.

Supersedes [!137] Fixes [#13]

See merge request [!143]

  [!137]: gitlab.dune-project.org/NoneNone/merge_requests/137
  [#13]: gitlab.dune-project.org/NoneNone/issues/13
  [!143]: gitlab.dune-project.org/staging/dune-uggrid/merge_requests/143


Closes #13

The old helper variable parallel was
removed by accident.
UG_PARALLEL is set to "True", no longer to "yes".

Similar to other Dune modules

The files were for compatibility only. They are
superseded by files created for any Dune module.

Delete parallel/.

Couple of links, only for backwards compatiblity with ug 3.13

Remove unused subfolder dom/gen/ and its content.

But it remains meaningless

Merge branch 'get-rid-of-uggrid-heapsize' into 'master'

See merge request [!142]

  [!142]: Nonestaging/dune-uggrid/merge_requests/142

This option used to be the heap size, but ever since we started
using the system heap for everything that size does not get
used anymore.

It is not used anyway.

Merge branch 'fix_warnings_unused_function' into 'master'

ref:staging/dune-uggrid Added preprocessor if-conditions and commented out
some unused functions to avoid compiler warnings made by CI test
"gcc-7-14-sequential".

See merge request [!127]

  [!127]: gitlab.dune-project.org/staging/dune-uggrid/merge_requests/127

Deleted the function "CheckNodeContext" because it was not used in.
````
static INT CheckNodeContext (ELEMENT *theElement, NODE ** NodeContext)
{
  INT i, mark,nor,noc;

  mark = MARK(theElement);
  for (i=CORNERS_OF_ELEM(theElement); i<CORNERS_OF_ELEM(theElement)+EDGES_OF_ELEM(th       eElement); i++)
  {
    if (NODE_OF_RULE(theElement,mark,i-CORNERS_OF_ELEM(theElement))) nor = 1;
    else nor = 0;
    if(NodeContext[i]!=NULL) noc = 1;
    else noc = 0;
    if(nor!=noc)
      if (GetNodeContext(theElement,NodeContext)) REP_ERR_RETURN(1);
  }
  for (; i<CORNERS_OF_ELEM(theElement)+EDGES_OF_ELEM(theElement)+SIDES_OF_ELEM(theEl       ement); i++)
    if (NodeContext[i]!=NULL)
      if (GetNodeContext(theElement,NodeContext)) REP_ERR_RETURN(1);

  return (0);
}
````

Deleted the definition of "CheckLocalElementKeys" for the case
````
!(MGIO_DEBUG>0)
````
because all uses in this file are contained in a preprocessor if condtion ensuring
that
````
MGIO>0
````

The function was not needed.

Added a preprocessor if condition around the definition of
"Write_RefRules" because it is used in such an environment.
````
static INT Write_RefRules (MULTIGRID *theMG, INT *RefRuleOffset, INT MarkKey)
{
  ...
}
````

Furthermore there is a comment adressing the only use of "Write_RefRules".

````
/* TODO (HRR 971209): drop old call of Write_RefRules */
  #if EXTRACT_RULES
if (NEW_Write_RefRules(theMG,rr_rule_offsets,MarkKey,&rr_rules)) REP_ERR_RETURN(1)       ;
      #else
if (Write_RefRules(theMG,rr_rule_offsets,MarkKey)) REP_ERR_RETURN(1);
      #endif
````
But i am not sure whether "Write_RefRules" is still needed.

Added a preprocessor if conditon around the definition of "FillSonPaths"
because the only use in this file is contained in such an if condition.
````
 #ifdef __THREEDIM__
static void FillSonPaths (MGIO_RR_RULE *rule)
{

 ...

}
 #endif
````

````
        #ifdef __THREEDIM__
  /* 2D: not even in rm */
  /* son path */
  FillSonPaths(mr);
        #endif
````

I added a preprocessor if-condition to the definition of "RuleCompare"
because the only use in "gm/er.cc" is contained in such an environment in line 698

````
 #ifdef __DEBUG_ER__
static INT RuleCompare (int id, const URULE *ur, const ERULE *er)
{
  ...
}
 #endif
````

````
        #ifdef __DEBUG_ER__
  ...
  RuleCompare(ID(elem),ur,er);
  ...
        #endif
````

I added a preprocessor environment to contain the definiton of the
function: "CheckElementContextConsistency"

````
 #ifdef Debug
static void CheckElementContextConsistency( arguments )
{

 ...

}
 #endif
````
because the following use of the function is also contained in such an
environment.