Deleting account does not wipe usage quota cache

[Rory-Powell]

Describe the bug As a part of account deletion all databases are deleted manually. This bypasses the normal event pipelines for removing apps, users etc. This means that the writethrough cache remains in place and upon re-signup the previous cached quantities remain. This scenario is not recoverable as there is no way to sync the quotas to the new count.

Expected behavior When an account is deleted the writethrough cache item for quotas is also deleted