Don't reload emotes directly into the global common.Emotes variable.
Instead, load them into a new variable and write that to common.Emotes
after the search for new emotes completes. Emotes should no longer
duplicate for each run of `/reloademotes`.
Also tweaked `/addemotes` to automatically reload emotes if nothing went
wrong downloading a new set.
This reworks how emotes are cached in relation to their physical
location on disk. Functionally, they should be the same from the user
perspective but it sets up some stuff that will make it easier to add
emotes from various sources.
This command launches a goroutine that does the actual downloading of
the emotes so the client doesn't hang until the process is finished.
subscribers.json needs to be manually downloaded and added next to the
main executable for now. Eventually, it will download and cache this
file (for 24 hours, at a minimum).
Issue #10 should not be considered finished yet. This needs to be
tested a bit more with multiple channels. Ideally, some that exist and
some that don't to verify that it fails gracefully (ie, adds the emotes
it was able to download).
