Deprecate constructor GeometryType(int)

As decided at the 2018 dev meeting in Stuttgart.

This constructor (and its cousin GeometryType(uint)) are not
really needed with the new way to construct GeometryType objects.

CHANGELOG.md

 # Master (will become release 2.7)
 
+- The methods `GeometryType(int)` and `GeometryType(unsigned int)` have been deprecated
+  and will be removed after the release of dune-geometry 2.7.  Instead, please now use
+  `GeometryTypes::cube(dim)` to construct one- or two-dimensional `GeometryType` objects.
+
 # Release 2.6
 
 - The enum `GeometryType::BasicType` is deprecated, and will be removed after Dune 2.6.

dune/geometry/type.hh

@@ -387,6 +387,7 @@ namespace Dune
     }
 
     /** \brief Constructor for vertices and segments */
+    DUNE_DEPRECATED_MSG("GeometryType(unsigned dim) is deprecated in DUNE 2.7, please use Dune::GeometryTypes::cube(dim) instead")
     explicit GeometryType(unsigned int dim)
       : dim_(dim), none_(false), topologyId_(0)
     {
@@ -397,6 +398,7 @@ namespace Dune
     // We need this constructor for "int" and "unsigned int",
     // because otherwise GeometryType(int) would try to call the
     // generic GeometryType(TopologyType) constructor
+    DUNE_DEPRECATED_MSG("GeometryType(dim) is deprecated in DUNE 2.7, please use Dune::GeometryTypes::cube(dim) instead")
     explicit GeometryType(int dim)
       : dim_(dim), none_(false), topologyId_(0)
     {