Fixes: *really* show box 1 second later; remove unneeded mw
Generalize 'color-mode' option and add sepia setting

This needs a bit of work (read: class specificity) to prevent messing
up the mw-mf-page-left sidebar. Also, should we add some sort of check
to avoid showing the option when filter isn’t available (*cough*
firefox *cough*)?