Get Trakt trending show images from TVDB (#3368)

* Get trakt trending show images from tvdb

* Remove useless logging statement

* Async load of trending trakt show images

* Fix build errors

* PoC: A hacky way of getting images simultaneously.
Definitely NOT the way to solve this.

Also, that `retry` decorator on tvdb_api isn't compatible with Tornado's async calls.

* Make async load work without request queue

* re.sub to str.replace, warning to debug