R1:e01ceaa07f4c

Provide 'bin/cache', for managing caches

Summary:
See <https://github.com/facebook/phabricator/issues/323>. We have a very old cache management script which doesn't purge all the modern caches (and does purge some caches which are no longer in use). Update it so it purges all the modern caches (remarkup, general, changeset), no longer purges outdated caches, and is easier to use.

Also delete a lot of "this script has moved" scripts from the last few rounds of similar cleanup, I believe all of these have…