tmdb: Add support for creating combined requests

Using the append_to_response parameter. This allows cutting down
on the number of network requests.

https://bugzilla.gnome.org/show_bug.cgi?id=723149
tmdb: Combine detail request calls

Reducing the typical "everything" request from 5 calls to just 1.

https://bugzilla.gnome.org/show_bug.cgi?id=723149
tmdb: Fix tests

https://bugzilla.gnome.org/show_bug.cgi?id=723149