OS X bundle: add UTImportedTypeDeclarations

Allows to declare UTIs [1] for types of file that OS X doesn't know, like mkv,
mka, etc.

For example: instead of having a dynamically generated UTI for .mkv like
'dyn.somerandomstring', 'io.mpv.mkv' is registered and conforms to public.movie
and is known system wide.

Note: The list is far from being complete but it should cover the most used
type of files.

[1]: https://developer.apple.com/library/ios/documentation/FileManagement/Conceptual/understanding_utis/understand_utis_conc/understand_utis_conc.html#//apple_ref/doc/uid/TP40001319-CH202-CHDHIJDE

Fixes: #734