webkit: add options to support up to 2.7.2
webkit2: handle the '4.0' pkg-config files
webkit2: remove page_view_mode from 2.5.1+

Remove upstream.
css: support the user manager in 2.5.1
navigation: provide is_gesture

Also support 2.5.2.
status_background: avoid deprecated functions

*sigh*
build: fix a build failure

Not worth figuring out why.
variables: add a missing function