Deprecate Algorithm::begin/endRun

This re-applies GMR gaudi/Gaudi!542 (merged) and gaudi/Gaudi!666 (merged)

Algorithms should not know about begin and end run transitions, as these concepts become fuzzy if not entirely meaningless in an environment where multiple events are processed concurrently. In the vast majority of cases, anything done in Algorithm::beginRun can be migrated to Algorithm::start, and endRun -> stop.

We also print out a warning message if a derived Algorithm implements beginRun or endRun, so as to ease migration of serial jobs.