URL Shortener plugin

[morganfshirley]

URLs that are too long wrap around the screen, making it difficult to click on them. Hamper should have a URL shortener to help with this.

[mythmon]

Relatedly, we have this, but it isn't enabled in #osu-lug because at one point it didn't work. We could work on making this work on our instance again. hamper/plugins/bitly.py.