breakpoints v2

See issue !172 (merged)

• fix bugs in breakpoint
• some breakpoint code refactor (Experiment mostly, also lightly job-strategy-aggregator), including trying to better separate breakpoint code between classes
• new handling of experimentation files: one unique folder with one copy of files that need to be kept after experimentation execution completes, link to files from breakpoint directories
• collateral: update/fix in unit test process and existing tests for other classes, write heavily-mocked tests for Experiment() breakpoint

General trend: breakpoints could be further refactored, but we probably dont want to spend more time now + some points may be better addressed after general refactor of Experiment()