Refactor/remove calibration_cathment.py and re-enable explicit strategey.

[hellkite500]

PR #130 introduced breaking changes which effect the explicit calibration strategy. As it exists now, the explicit strategy is not very optimal, as it runs the entire calibration look (including model execution) for each calibration_catchment explicitly defined by the realization. This can be done more efficiently with a many-to-many connection of calibration features with evaluation features and a smarter implementation of the search space semantics, similar to the independent strategy.

The calibration_catchment needs to be deprecated and removed and the explicit strategy refactored to implement the intended semantics via, likely, a list of CalibrationSets of size one.

[aaraney]

Just to note here for people who could run into issues, CalibrationSets does not support model plugins at this point in time.