[Proposal] Allow queuing of password reminder emails

Per #2301& #2693:

Adds a parameter on to `remind()` and `sendReminder()` to allow queueing of password reminder emails. If the parameter is set to `true`, `Mail::queue()` is used instead of `Mail::send()`; if the parameter is a string, `Mail::queueOn()` is used with the parameter as the queue name.