Moved CbmStsDigitizeQa, CbmStsDigitizeQaReport and CbmStsFindTracksQa to qa...

Moved CbmStsDigitizeQa, CbmStsDigitizeQaReport and CbmStsFindTracksQa to qa subfolders. Updated CMakeLists.txt accordingly.

Comment: May require deletion of "CbmStsSimDict" and "CbmRecoStsDict" library files in build directory to trigger recompilation.

Suggested reviewer: @f.uhlig