Added support for WDTV compatible metadata.

First pass at WDTV metadata.  Seems to correctly write out xml files for episode metadata, .metathumb files (jpegs) for episode stills and series images.

Currently not correctly writing out season images, but submitting pull request so other developers can comment on my code.

Also need to address how we match season images - this relies on a hard coded regex which isn't ideal.