[Tracker] Media art detection

[Sam Thursfield <ssssam gmail com>]

Good afternoon,

I just filed https://bugzilla.gnome.org/show_bug.cgi?id=660784 with a
rewrite of the album art detection code, which now supports detecting
video posters as well.

It seems like it would make sense to s/albumart/media_art over the
code base, anyone in favour?

Also, I wrote a couple of unit tests for the
tracker_albumart_find_external() function, but using it requires
moving the tracker-albumart functions into libtracker-extract instead.
Which would be fine except it requires TrackerStorage which is in
libtracker-miner, which would introduce a dep in libtracker-extract on
libtracker-miner. Any ideas on this one? It seems the options are
  1) move TrackerStorage into libtracker-common
  2) come up with a way of exposing functions in tracker-extract for testing

And as a final thinking point, wouldn't it be nice if we could have an
nie:MediaArtImage class so that when a file is decided to be media
art, there's no danger of it showing up in searches for photos etc?
I'm not entirely sure what the best way to do this would be.

Sam