Metadata tweaks and updates

* Lots of cleanup to make things a bit more standardized.

* Remove **Synology** metadata since it was just a clone of MB and does not appear to be actually used by synology units.

* Add `banner`, `season banner` `season all poster` and `season all banner` options. 

* Remove `use_banner` poster override since now we have a `banner` option. 

  > This now means users can have **both** a poster and banner instead of one or the other (**XBMC12+**).

  * Migrate legacy **XBMC** `poster` + `use_banner` setup to just `banner` option (keeps old functionality).

  > Notice that on **XBMC** the banner and poster result in the same name, if you have both checked off it will just create folder.jpg with a poster since we don't overwrite existing metadata.