Open in SoundCleod

This PR adds a service for right click support to open SoundCloud URLs from any application in SoundCleod.

Right click a link/text containing URLs -> Click `Services` -> Click `Open in SoundCleod`. You can also assign a keyboard shortcut to open the selected object in SoundCleod through the system settings.

## Testing notes
* Services for newly installed apps are loaded when logging in to OS X, so after building the first time, one must log out and in once for the service to appear.

* If an application has a custom right click menu, it might not show Services (An example of this is Sublime Text.) You can always access the services by clicking the application name in the status bar, however.

## Issues
* When registering the service I use the "old" values for [Send Types](https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/SysServices/Articles/properties.html) (`NSStringPboardType` etc). The [NSPasteboard documentation](https://developer.apple.com/library/mac/documentation/Cocoa/Reference/ApplicationKit/Classes/NSPasteboard_Class/index.html#//apple_ref/doc/constant_group/Types_for_Standard_Data_OS_X_v10.6_and_later_) states that since OS X 10.6 we should use the new values (`NSPasteboardTypeString` etc) instead, but I was unable to get this to work. The old way seems to work fine for now. If anyone else wants to experiment with this, please go ahead :)

* The service will show up in SoundCleod too, but won't actually do anything. I don't think it's worth spending too much time on since it won't be needed within the app.

## Other notes 
This PR probably renders the cleod://-scheme obsolete. We should consider removing it unless we intend for other apps to be able to communicate with SoundCleod in the future.