Move identicons grid to a directive
Add `SparkMD5` to jshint globals

This tells jshint not to raise an "undefined" error on `SparkMD5`. This means
that `window.SparkMD5` can be changed to just `SparkMD5` without making jshint
raise an error.
Implement `identiconUrl.fromUserId` service method

This encapsulates the logic for converting a GitHub user's ID into
the URL for their identicon.
Use `identiconUrl` service in `MainCtrl`
Implement `organizations` route

This takes you to a page where you can see the identicon of every
user that belongs to that organization.