Add full series mark

[OttoKerner]

As far as I understand it, this is just the opposite of this existing feature request.

Option to show MISSING seasons and episodes

I have access to a friends shared library and every time I go into a episode "folder" I have to carefully look if there are missing ones before starting to watch anything(I hate starting to watch a show, to only find out that there are missing episodes in-between them all).   It would be so much easier is there was an option in Plex, that the client could turn on/decide if he wants to show missing episodes ("Make missing episodes visible") The missing episodes could be just listed as normal o…