Reworked import of runtimes from .nfo files

Hi Guillaume,

this is a reworked version of my last PR. If a runtime is detected in tvshow.nfo this will be set as runtime on series level in plex. If not, the median of the episode runtimes will be used, like you suggested. I tried to update a single episode. This has no negative effect, as it seems to trigger a full update for all episodes.

Please have a look at it and comment.