Allow choosing which antifeatures to show

Part of admin#252.

Fixes #564 (closed) when done.

TODO:

• Deal with the introduction of new antifeatures - The default is set in app/src/x/res/xml/preferences.xml and currently contains every single antifeature. When we add new antifeatures we don't want to enable by default, we can edit the default. It will only affect users who haven't manually changed their settings)
• Actually hide apps completely when shown is set to off (and always display Anti-features text?)
• Figure out why Settings in the bottom doesn't get highlighted when clicking on hidden apps notice
• Scroll to antifeature settings?