Handle the `cleod://` url-scheme

This pull request handles the `cleod://` scheme. Replace `http`/`https` in any SoundCloud URL and it will now be automatically opened in SoundCleod instead of a browser tab.

This partially solves #46. To automatically redirect web links to SoundCleod we need browser extensions that replaces `http`/`https` with `cleod` when clicking a SoundCloud-URL on any external page. I will start working on a Safari-extension that does this, and when I get it working it shouldn't be very hard to port it to Chrome etc.