Add Objective-C header for MPlayerX Apple Script interface

Generated with:

sdef /Applications/MPlayerX.app | sdp -fh --basename MPlayerX
Add support for MPlayerX

Supporting movie name requires additions to MPlayerX scripting suite
which I hope to look at sometime soon.
Support for title and URL in MPlayerX

Requires changes to MPlayerX proposed in:

https://github.com/niltsh/MPlayerX/pull/26

Code degrades gracefully if MPlayerX does not have these changes (behaves
as if this commit is not present).
Merge pull request #6 from dusek/mplayerx

Support for MPlayerX