media-manager: Use correct tracker language property

In the end, it was decided not to make the existing 'nie:language'
property multi-valued but rather introduce a new custom property for
this case, 'osinfo:language'.

This patch also:

* moves the handling of Tracker SPARQL query into a seperate
  module/class, TrackerISOQuery.

* ensures compatibility with older Tracker (that doesn't extract and
  expose the new 'osinfo:language' property) by using different queries,
  depending on whether or not 'osinfo:language' property is known to
  Tracker.

* ensures language info is extracted from media if its available in case
  of older Tracker and therefore ensures that we don't end up using a
  locale that media doesn't support and break express installation.

https://bugzilla.gnome.org/show_bug.cgi?id=729122