Added URI scheme handlers: mms, rtmp, rtsp

Added URI scheme handlers: mms, rtmp, rtsp

URI scheme handlers allows VLC to manifest ability to open these URIs.
Practically it means that if user wants to open url like
mms://example.com/ system may automatically choose VLC to open it.

I haven't included http, ftp, etc. because they are better handled by
web browsers than media player.

More info about URI scheme handlers are here:
http://standards.freedesktop.org/shared-mime-info-spec/shared-mime-info-spec-latest.html#id2869854

Line with MimeType key is now longer than 998 characters (see RFC 2822).
I haven't found a way of making it shorter. In case you didn't get whole
line it ends with: x-content/audio-player;application/xspf+xml;

Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>