WIP: General Broken Lines

This is only a WIP MR adding a general broken line as an optional fit model. There is still a lot of work/clean up required - comments and suggestions are welcome.

New features:

• General broken lines, ignoring rotations around x/y.
• "track" class is used as a base class to derive new classes StraightLineTrack and a GBLTrack.
• Build option BUILD_GBL to use corry on any system.

I am not really happy with the class names and open for suggestions. Currently, rotations are ignored.

There are still missing pieces (Feel free to add toDos here):

• Test if the new StraightLine implementation provides the same results as the Standard track.
• Improve naming
• Implement an state() and direction() function for the GBL
• Fix the CI problems
• Provide a test data set
• Rotations