chore(cache): Add some nice new internal APIs for caching

This *greatly* simplifies caching logic, especially for memcache-related code. See Datalist.php for the example in this PR.

TODOs:
- [ ] Implement incomplete tests
- [ ] Add back memcached et al support
- [ ] Add tests for refactored classes
- [ ] Split into 2 PRs/commits -- one to add new APIs, another to actually use them in existing classes
- [ ] Deprecate old Caching classes in favor of new ones
Ah I see. `*` is not an alias for "all keys", it's just another key meaning everything pulled from the table. So it must flush the individual key in case that was set during the request.