2nd phase of reworking

Added `songSets` and `bots` collections to config.
Simplified `randomFromArray()`
Implemented `getArtistTitlePair`
Renamed some variables for clarity/accuracy
Rough refactoring to call `makeLyrpicTweet()` with a `bot` object

TODO:
Implement initialization (check config for `bots`, call
`setInterval(makeLyrpicTweet(bot),bot.interval)` for each, &c)
Compartmentalize/clean up
Rework `getRhymes` and related functions