Refactor task chain up to limits
This PR refactors the task chain to create limit plots. Most important changes:
- Added
MultiDatacardBaseTask,POITask1DWithRandPOIScanTask1DWithR - Encoded hash of input datacards into output paths
- Added two new plots (
PlotMultipleUpperLimits,PlotUpperLimitsAtPOI) for comparing limits across configurations - Updated docs accordingly