Store app config in Application Data

[remixz]

This fixes GH-7.

atom-shell has some cool utilities in place to handle config folders (https://github.com/atom/atom-shell/blob/master/docs/api/app.md#appgetpathname), so this makes monu use it! I also updated the call to open the config folder to use open, since it handles a bunch of cases for escaping paths, such as those with spaces in it (which we now have!).

Also, there's now an npm script (npm run app) to run the app, which makes sure that while developing, it always loads the package.json with the product name, which is needed for the config folder.

[remixz]

Aha! Turns out atom-shell has its own way to open folders/files built in: https://github.com/atom/atom-shell/blob/master/docs/api/shell.md#shellshowiteminfolderfullpath. Using that as of a6590db

[max-mapper]

WOOOOOT! Thanks a bunch, Zach