Add special handling for Omnibuses

[Casvt]

Is your feature request related to a problem? Please describe.

Kapowarr can detect special versions like one shots, TPB's and hard covers. But there is no handling for omnibuses. This means that sometimes it will download the omnibus for a normal volume, which is not desired.

Describe the solution you'd like

Make omnibuses a special version too (= add it to the 'special version system'). Only download and match omnibuses when the volume is for one too. Otherwise deny.

Additional context

Add 'omnibus' to the list, make the file_extraction.extract_filename_data() function detect omnibuses, expand some matching functions, and you're pretty much there.