FIX: on mobile view, never show the show/hide preview link in composer. nexus 7 was showing it.
FIX: z-index issue with quote reply button on mobile
FIX: mobile style of edit reason input
FIX: detect css changes in plugins that use register_css
Revert "disable google, twitter, facebook logins by default"

This reverts commit d7f62f71486b7b96ac158be54bb3da631194b565.
New site setting: `limit_suggested_to_category` - ensures suggested
topics belong to the same category as the current topic and doesn't mix
in other categories.
Merge remote-tracking branch 'upstream/master' into feature-people