Allow default paths for opencascade detection

OPENCASCADE_DIR is just a hint and might be invalid.

(In FindTRILINOS.cmake the full path is known due to the inclusion of the
Trilinos project configuration. Thus, those options ensure that no wrong
library is accidentally picked up.)
Merge pull request #244 from tamiko/fix_opencascade_detection

Allow default paths for opencascade detection
added read support for step files, along with its tests. write support is a little bit more complicated, we'll work on it
added write support (with tests) for step files
Fix GridTools::distort_random for distributed meshes
Minor documentation update. Reorder two functions.
Move communicate_locally_moved_vertices to parallel::distributed::Triangulation.
Add a test for communicate_locally_moved_vertices and verify that its output is correct.
Introduce GridTools::get_locally_owned_vertices().

Also use it in an existing test and in an assertion.
Revert to the old code for the sequential case to maintain backward compatibility. Adjust testcases.

Minor reworks.
added namespace and () to the read_STEP and write_STEP name functions in the doc/changes.h file; removed some extra empty line from the function implementation in utilities.cc
Merge pull request #245 from andreamola/added-STEP-support

Added step support
Merge pull request #239 from bangerth/parallel-distort-random

[WIP] Parallel distort random