ctest support added. test/CMakeLists cleanup

[tarTG]

Added ctest support.
Tests can be started with make test
removed unnecessary stuff from test/CMakeLists.txt

[ftomassetti]

Thanks. Travis seems unhappy about this PR but I am not sure why

[tarTG]

The Python 2.6.9 build used old dependencies. There are updated now.
In all the clang builds with Python, Python could not find the clang compiler. Even in the stable builds, clang was never used. I did a workaround by reinstalling clang, but I think we have to restructure the build matrix in Travis to have a nice and clean solution.

[tarTG]

Set compiler on Travis to gcc-6 and clang3.7
CMake is now building with C++14 on all compilers (including MSVC).

Also forgot to squash the branch... sorry for that