R1:9292433daebd

Implement "Resign" action against ApplicationTransactions

Summary:
Ref T2222. This introduces two small new concepts:

- `expandTransactions()`: allows a transaction to expand into several transactions. For example, "resign" adds a "remove reviewers" transaction.
- We have some other cases which could use this, but currently hard-code things outside of the `Editor`.
- One example is that in Maniphest, closing a task implies claiming it if it is unowned.
- `setIgnoreOnNoEffect()`: The whole…