Dark theme

[Kenny2github]

Many changes in this branch, mostly in CSS. Preview these changes on https://oauth2.scratch-wiki.info (where the dark theme is forced in use).

New Stuff

• New user preference to enable dark theme
• New configuration variable to force dark theme
• If either are enabled, or if a media query says the viewer prefers dark color schemes, the dark theme class is added to the body
• Tons of new styling applies to children of .dark-theme (mostly overriding MW styles)
• Dark theme has feedback footer

Minor Changes

• Search box now has internationalized hover text
• Search box now only unexpands when clicked out of
• Internationalization cleanup

[Kenny2github]

Note to merger: Squash when merging

[jacob-g]

It automatically went to dark theme without me setting anything. so let me see if my browser automatically prefers dark theme (if so it's functioning as intended).

[Note: There is a bug. See my review comments for details]

[Kenny2github]

Got rid of light theme footer