This adds a dependency on housekeeping, our new deprecation management

library, and switches all of our base classes over to it.
The original base class and deprecation utility functions are still

there, but wrap the versions in housekeeping. They themselves are marked

as deprecated and will be removed in Djblets 6.
The BaseRemovedInProductVersionWarning is deprecated, but remains for

now. We can't mark it as moved or deprecated using housekeeping, given

circular references (which Housekeeping 1.1 was supposed to fix, but

ultimately couldn't).

Unit tests pass in Djblets and Review Board.