Verify token caching

[joshtrichards]

There's chance that caching is being handled in an inconsistent way in the Push class:

• neither of the deletePushToken*() methods directly update the cache; both rely on the caller to handle that
• not all instances where deletePushToken*() methods are called update the cache
• the PushController class has some overlapping functions with Push that do direct DB updates/inserts. That further complicates things.
• the PushController class isn't even aware of the cache used by the Push class

Impact:

• based on the expiration time used for the cache in Push::validateToken() at a minimum it's possible for there to be a discrepancy for re-registered devices of ~10 minutes (I think)
• duplicate code in Push and PushController classes increases code maintenance burden as well as inconsistencies/bugs

Disclaimer: It's possible the cache matter is prevented in some other way; I don't have time to get too deep into this today, but wanted to note it since it seems to be the case.