Revert back to TVRage for now:

 - now that TVRage is back up again, use it.
 - TheTVDB needs work still, e.g. searching for shows with years in the title, like House of Cards (2013), doesn't resolve to anything.
Added GlobalOverrides:

 - currently it's read only, to add a show to the overrides edit the ~/.tvrenameroverrides file (xml).
 - a default set of overrides (Archer, The Newsroom, House of Cards) will be written on load if there is no overrides file already.
 - refactored (rename some things) existing persistence stuff to be more consistent.