Add entry for url protocol

add mpv:// for url protocol handling
Add URL protocol handling

As said on IRC, it was just a test to support url protocol handling
(mpv://some-ur-to-a-movie) the code is kinda ugly, but it should work.
Probably need to launch mpv a first time to register the protocol
handler with LaunchServices. If it doesn't work resetting LS with the
following command should do :

/System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServi
ces.framework/Support/lsregister -kill -r -domain local -domain system
-domain user