Globally required words

Repeating this PR. Please reconsider.

Added support for globally defined required words. Functionality is opposite of globally defined ignored words. Sets of required words can be defined in search settings. Releases must match at least one set of required words to be accepted. If no required words are defined, all releases are accepted for this test. 

Enables users to specify a global filter for all releases, and for example select only releases from a specific scene group, only releases with subtitles of a certain language, or only releases of a certain language (or any of the examples combined).

Example:

Required words: swesub&720p,swedish&publichd

Only releases containing both "swesub" and "720p" OR both "swedish" and "publichd" are accepted.