[export] Print bounding radius of exported file to standard output
Move resolve_file_path function to zusicommon
Add Ls3File object to prepare for exporting multiple files
Use new Ls3Subset class for mesh subsets
Export to multiple files as preparation for animation export
Add test for correct export file name, allow setting optimizeMesh and exportSelected args in tests
Write empty <Animation> nodes
Set AniBeschreibung attribute
Add <MeshAnimation> nodes
Add <VerknAnimation> nodes
Fix test for animation export and add a second test
Initialize LSB writer at the beginning of each LS3 file
Modify second animation test for better test coverage and make it pass.

The test is now the same as the first animation test, except that the Empty is
at position 0/0/0 and the plane has no constraint. Thus only one linked file
should be created.
Write <Animation> nodes correctly with AniId and AniBeschreibung attributes
Write <AniNrs> nodes in <Animation> node
Refactor animation number calculation
Unify test case names
Write <AniPunkt> nodes and AniZeit values
Write some rotation keyframes
Fix capitalization of 'AniID'