Separate out intent handlers

[ianb]

We should make an intents/ directory in the extension, and each intent should go in there. We should use one directory per "category" of intent (e.g., there is a play music and pause music, but they would both be in a music/ folder).

For now I think it can be as simple as, say, intents/find/find.js (I find a kajillion index.js files a bit hard to handle, so I'd rather clone the directory name as the main file).

[ianb]

This was fixed in #52