Submitting WIP to Master

Moved from a single `lyrpictweet.js` to a structure featuring `credentials`, `songSets` and `bots` objects set in `config.js` for API keys, aritst/title pairs, and configurations for bots using different Twitter accounts/Flickr tags/music genres.

Revamped logic in `lyrpictweet.js` to create `Bot` objects based on the settings in `config.js` and start each with its own intervallic call to `makeLyrpictweet()`, staggered.

Various other changes in logic/flow.