Fix date and revision on git

Added a small CMake module GitInfo, since the actual Git module doesn't provide repo infos.

Added variables SEQAN_DATE and SEQAN_REVISION to FindSeqAn.cmake. I refrained from adding these variables to SEQAN_DEFINITIONS because few CMake targets would use them.

Fixed the search/join apps to show how the fix looks like. All other apps have to be fixed.