Support .nfo metadata

.nfo XML metadata is a fairly common format. For example Kodi will notice it in a folder and use that to identify the show. Using this data if available could provide a more reliable source of metadata without needing to falling back to searching and guessing.

An example file could look like this:

<tvshow>
  <title>Rick and Morty</title>
  <rating>9.3</rating>
  <plot>Follows the misadventures of an alcoholic scientist Rick and his overly nervous grandson Morty.</plot>
  <mpaa>TV-MA</mpaa>
  <id>275274</id>
  <uniqueid type="tvdb" default="true">275274</uniqueid>
  <uniqueid type="imdb">tt2861424</uniqueid>
  <genre>Adventure</genre>
  <genre>Animation</genre>
  <genre>Comedy</genre>
  <genre>Science Fiction</genre>
  <premiered>2013-12-02</premiered>
  <studio>Adult Swim</studio>
  <actor>
    <name>Justin Roiland</name>
    <role>Rick Sanchez</role>
  </actor>
  <actor>
    <name>Justin Roiland</name>
    <role>Rick Sanchez</role>
  </actor>
  <actor>
    <name>Justin Roiland</name>
    <role>Morty Smith</role>
  </actor>
</tvshow>