add control port buffer so setEvents() can be called anytime

I just had an idea that I think will cover this issue, be relatively easy to implement, and replace this pull request:

* accept setEvents() calls any time
* if the control port is not active, cache the value of last setEvents() call
* after TorService receives the first CIRC event, send the cached setEvents() value
* further setEvents() calls are sent directly to the control port
* this buffer should probably be a queue that stores all recieved messages in order and replays them
* when TorService sends `STOPPING` and `OFF`, the queue should be cleared.

This should allow setEvents() calls to work any time.

@n8fr8 @bitmold Should it queue events when it is `OFF`? Or only when `STARTING`?