This silences a few warnings when compiling with -DNDEBUG.

[bugfix][adaptivity] Remove isNew markers on ALL levels

When global refining not all isNew markers were removed.
This also caused a bug when mixing growth and adaptivity as the
isNew marker is also used for newly added elements through growth.

If merged this needs to be backported to the 2.4 release branch!

See merge request !8

[cleanup] Remove deprecated Dune::remove_const with std::remove_const



See merge request !9

When global refining not all isNew markers were removed.
This also caused a bug when mixing growth and adaptivity as the
isNew marker is also used for newly added elements through growth.

Feature/update to dune 3.0

This is based on merge request !4 

See merge request !7

[fix] Remove hides virtual overload warning



See merge request !6

Update Readme and license in markup



See merge request !5

Feature/setposition

Implement a setPosition method for vertices.
This branch is based on the feature/growth-revised, so !2 should to be dealt with first.

See merge request !3

Only leaf vertices can get a new position. However this
triggerts that the vertex' position on all levels will
be changed accordingly.

Add a setPosition test.

Feature/growth revised

Implement the new growth interface. It mimics the grid factory and combines it with the adaptivity interface.

See merge request !2

For consistency with the factory.

When the final insertion level for vertices and elements was
determined for an element that is unconnected to the elements
of the current grid the level was initialized to numerical_limits::lowest.

This makes sure the lowest level is zero

Adds a test that checks inserting an unrelated element.

We use the ID later to determine whether new vertices are
used by multiple elements.

Using up ids for entities that are not inserted in the end made the idSet fail
to contain all entities for some reason.