Exclude certain namespaces from the default enabled/disabled discussions

Based at the work of https://github.com/NikolausL, Thank!

https://github.com/NikolausL/plugin-discussion/compare/dokufreaks:master...master#diff-3c55f5ee8584e7fd6e98541d4ee3f92dR354
Merge remote-tracking branch 'upstream/master'
Feed plugin uses the 'threads' lang string
reformatting and notes
Merge pull request #149 from Klap-in/master

repo cleanup