Clang is now called AppleClang on Mac OS.
[IO] Specify full path in include.
[ML] Specify full path in includes.

Also removed unnecessary includes.
[ML/Tests] Fix warnings in tests.
[GL] Specify full path in includes.
[ML] Make all include paths explicit.
[ML] Include declaration headers first.
Merge pull request #498 from endJunction/FullPathInIncludes

Full path in includes
Merge pull request #499 from endJunction/FixWarningsInMeshLibTests

Fix warnings in MeshLib tests.
[NL] Add DIM, NPOINTS to all ShapeFunction classes.

The expressions are needed for local assembler matrix sizes.
[NL] Add default ShapeMatrices constructor.
[NL] Add Eigen fixed and dynamic ShapeMatrixPolicy.
[ML] Make elements' dimension a constexpr.

Needed for choosing integration method at compile time.
[NL] Add a GaussIntegrationPolicy.

Chooses regular gauss integration but for triangles.
[NL] Remove integration method from isoparam. FE.
[NL] Set integration method in TestFe explicitly.

For this test GaussIntegrationPolicy is used.
[ML] Add compile-time pow() for int exponents.
[NL] Add MeshElement type to ShapeFunctions.
[NL] Remove  T_MESH_ELEMENT from isoparam. FE.

This type is present in the shape function classes.
[T] Remove extra FeType struct using template alias.