## Summary
Spawning new threads in Java is costly. This MR aims to use a common thread pool instead.
I've replaced all cases where a new thread is started just to perform a task in the background. This does not include cases where a reference to the newly created thread is kept as a part of application logic – this is probably a problem in itself, but it exceeds the scope of this quick optimization. ;)
There was a couple of cases where a new thread was spawned just to sleep for a while an then change the state on a View on the main thread. I've replaced those with posting those deferred tasks to the View's message queue.
## Test Plan
Everything should work the same as it has before, just a bit faster and easier on the memory.
This also allows "unsending" packets (if they're still in the queue).
This patch does that for mouse move packets, so they get accumulated
together (sending less stuff over a congested link).
