Smarter file generation

[orlandoisepic]

This resolves #5

Changes

• A new class "StateTracker" has been added in precicecasegenerate/state_tracker. It maintains a dictionary storing hashes of created files.
• Remove rmtree from the participant-solver directories, i.e., they are not deleted anymore in order for manually created files to survive 🏄‍♀️

Details

• The state tracker tracks each generated file with its hash. If a user manually edits a generated file, the hash changes. Upon rerunning the case-generate, files with non-matching hashes are backed up to backups/current_time and a warning is displayed.
• Previously, participant-solver directories were removed completely before being generated anew. This leads to loss of manually created files. This is now changed, i.e., the directory is not removed anymore. Manually created files will thus survive a re-run.