Add TMDb request limitation handling

The TMDb API has a request limitation, which should be considered with in the API Wrapper.
If the limit is exceed you will receive a 503 HTTP error.

The API v3 was limited to 30 requests every 10 seconds per IP:
http://help.themoviedb.org/kb/general/api-request-limits

The current limitation (4 requests every 1 second per IP) is discussed here:
http://www.themoviedb.org/talk/512921ea19c2951d8124fb17