Add git and compiler information to output

Added git and compiler information to output, for easier reproduction of issues to investigate the right version of the program or directly hinting the user, that an update is needed. PeTrack now starts with:

Starting PeTrack
Version: 0.8.14
Commit id: f646c7f
Commit date: Wed Jan 6 18:14:32 2021
Build from branch: 97-add-git-info-to-output
Build with: g++ (10.2.0)

Also the about window is changed, now the information is displayed as:

Remark the contributors name in the about window are not touched, this should be done in #52 (closed).

Note: This also introduces a finer versioning for the files! From now on every change on the .pet file should also be reflected by changing the version number in the CMakeLists.txt and saving the tests files with the new version to check conflicts.

Closes #97 (closed)