Xbmc library scan/clean (experimental)

I'm not sure this plugin should be a part of Flexget, but I have tried XBMC Watchdog and XBMC Library Auto Update addons and they both suck in some ways.

What I want is some automatic library scanning whenever new content is added to my library folders. This plugin should be used with the `move` plugin or `find` etc. It can also be used in a task of its own, although Flexget will warn the user of missing filter plugins etc.

`dir` supports jinja. The JSONRPC API of XBMC is quite extensive. Plugin currently support scan and clean of audio and video libraries. It may or may not support all the API functions in the future although I'm not sure I see any use for it.

It's rather niche but I fully intend to use this plugin even if it does not get merged.