Support themoviedb API 3 and download basic images

The code is updated to support the version 3 API. As a side-effect
the is incompatible with the old version and will delete itself.
One image and one poster is always downloaded on add. To choose a
different image use get_all_images and get_all_posters.
Download series and season images on sync

The series and season background image, poster and banner are
downloaded on sync so they are present when needed.

API change: the properties images, posters and banner are replaced
by the properties image, poster and banner returning the path in the
local filesystem. To get all images use get_all[images|posters|banners)
Use the server show id for the image filename
make sure the file exists
Create image directory
adjust to thetvdb changes
adjust to parser changes
Avoid searching the same tv series multiple times
Make sure the beacon rescans the files on change

If an external application (e.g. webinfo or Freevo) is adding
a new entry to the database beacon should check all video
files for changes.

This still does not work in all cases. The whole idea of the
version file is kind of broken. We need something else.