Emote scraper rewrite

The emote scraper is now multithreaded ans _should_ be faster.
Also, the class based architecture allows easy extensibility for future
projects. To process the emotes for a different project another superclass of
AbstractEmoteProcessor can be added.
The scraper also does proper rate limiting, if it is configured to do so.

This pull request should cleanly apply to berrycardsagainsthumanity/berrymotes:extension