Rename BDM prebasis from 'bdm' to 'brezziDouglasMarini'

In an attempt to get towards a meaningful naming scheme.
The new name is the name of the global basis without the
'Basis' suffix and with a lower-case first letter.

dune/functions/functionspacebases/brezzidouglasmarinibasis.hh

@@ -409,7 +409,7 @@ public:
 } // end namespace BasisBuilder::Imp
 
 template<std::size_t k, GeometryType::BasicType basic_type>
-Imp::BrezziDouglasMariniPreBasisFactory<k, basic_type> bdm()
+Imp::BrezziDouglasMariniPreBasisFactory<k, basic_type> brezziDouglasMarini()
 {
   return{};
 }

dune/functions/functionspacebases/test/brezzidouglasmarinibasistest.cc

@@ -43,7 +43,7 @@ int main (int argc, char* argv[])
   // check RaviartThomasBasis created using basis builder mechanism
   {
     using namespace Functions::BasisBuilder;
-    auto basis = makeBasis(grid.leafGridView(), bdm<1, GeometryType::BasicType::cube>());
+    auto basis = makeBasis(grid.leafGridView(), brezziDouglasMarini<1, GeometryType::BasicType::cube>());
     test.subTest(checkBasis(basis));
   }