python: Add basic tmdb lookup scripts to retrieve artwork.

python: Add basic tmdb lookup scripts to retrieve artwork.

The scripts attempt a tmdb lookup by using the title+year from
the dvr record associated with a particular uuid.

It then sets artwork and fanart.

The script can either be invoked manually or run automatically
from Tvheadend when a recording occurs (pre-recording rule).
In that case it needs to be passed the arguments:
"/usr/local/bin/tvhmeta --uuid %U --tmdb-key abcdef"
...where the key is from the tmdb website sign up.

The tv_meta_tmdb library is stand-alone and can be used
to test specific lookups to determine why they do not work.

A per-user cache is kept inside the tmdb3 library and this
is stored in /tmp.

The tmdb3 library has to be installed. This can be installed via "pip
install tmdb3" or "synth install www/py-tmdb3" depending on OS.

The scripts support a "--debug" option. I'd expect we are likely to
get several wrong/no results, especially with non-English movies until
we have a larger set of failure reasons to work with.

Once we get the tmdb working, we can try and "modularize" it so
different providers can be installed, and add a grabber for tv
episodes.