CAD mapping algorithms for pyramid elements

[jfussbro]

Since t8code already covers CAD interpolation/mapping for quadrilateral and triangle elements (2D) and for hexahedra, tetrahedra and prisms (PR: #971), the last remaining element type is the pyramid.
A test for the pyramids already exists (PR: #1036 )

For this issue, tests have already been implemented at
[test/t8_geometry/t8_geometry_implementations/t8_gtest_geometry.cxx/DISABLED_t8_gtest_geometry_cad_pyramid, linked_faces]
[test/t8_geometry/t8_geometry_implementations/t8_gtest_geometry.cxx/DISABLED_t8_gtest_geometry_cad_pyramid, linked_edges].
Remember to enable the tests by removing any DISABLED_ in the names when you start working on this issue, or to use --gtest_also_run_disabled_tests during execution of the test.

[jfussbro]

The test is merged and the algorithm is in review.