Fix a buf that made "Custom query" impossible to erase in the metadata editor
js: Add support in javascript API for binding video metadata to items
glw: Rework syntax of propSorter() so it's much more flexible
Display subtitles in order of preference
js: Add showtime.xmlrpc() for doing XMLRPC requests
Fix missing locking
Add plugin support for subtitles

This also removes built-in support for opensubtitles.
It will be shipped as a plugin instead