Add snapshot functionality to all tasks

This tasks adds the feature to use initial workspace snapshots to all tasks. The usage of a snapshot is optional (yet probably recommended for unblinded results) and can be enabled by adding --use-snapshot. The dedicated task is called Snapshot and triggers a single MultiDimFit with the essential, significant parameters (e.g. --hh-model, --datacards, --unblinded, --pois, --parameter-values, ...) passed from upstream tasks. This way, the same snapshot can be shared across different steps. Additional improvements coming with this PR:

• Easy configurable default hh module and model
• Improved coloring of combine commands
• Several minor plotting improvements