Rework: Representative Snapshots

[sstroemer]

Collection of ideas, notes, etc. on reworking the current representative Snapshot version (that was in some ways similar to one in SpineOpt).

Related issues:

• Missing functionality in unit commitment #23

[sstroemer]

• Example 30 is currently disabled (in tests).
• If we remove the current representative snapshot formulation (and change to another one) we could see if a "simple" snapshot aggregation feature in the form of fixed resampling could be possible (now as actual feature, not as dev feature)