Update wdtv.py to fix formatting

Several display elements on WDTV Live units do not display due to improperly formated xml, some minor tweaks fix all that.

Added runtime element to display runtime on WDTVs
Corrected firstAired to create a 'year' tag so as to be correctly read by WDTVs
Corrected actor structure to create separate actor element with name and empty role subelements for each actor so as to be correctly read by WDTVs