ContrastHigh: Style .background, not GtkWindow

We want to be able to simulate a regular window background by just setting the background style class.
ContrastHigh: improve style for insensitive colors

Set a global insensitive color, so that applications that assume it's different from the regular text color don't get black when querying a color from the theme.
HighContrastHigh: add style for linked vertical button boxes

As seen in gnome-packagekit.
ContrastHigh: add theming for OSD progressbar

As seen in Epiphany and gnome-online-accounts.
ContrastHigh: improve styling for floating-bar widgets

Add a border and round it according to its position.
ContrastHigh: add support for CSD and headerbars
ContrastHigh: fix Nautilus styling
ContrastHigh: fix insensitive menu items
HighContrastHigh: add a style for hovered listbox rows
ContrastHigh: don't set a frame on GtkStatusbar
ContrastHigh: add missing selector for image-button classes
ContrastHigh: update metacity-theme-3.xml
Merge pull request #53 from NiceandGently/master

ContrastHigh: update to GTK3-3.10