StButton is used for many things - scrollbar steppers, etc. Theming
all buttons to look like push-buttons breaks that. So in testcommon.css
just theme a .push-button class to look vaguely button-like.
https://bugzilla.gnome.org/show_bug.cgi?id=596432
Remove the StBoxLayout:spacing GObject property, and instead make
BoxLayout look up the spacing from the CSS style. This makes it
consistent with padding and will allow the use of units. (The
removal of the GObject property entirely instead of making it an
override is consistent with how we handle color, font, padding, etc.)
https://bugzilla.gnome.org/show_bug.cgi?id=596803
Use BigRectangle to draw the border and background if there's
a border width or border radius and no border image. (Only
uniform borders are supported for now with some deviations
from the CSS model noted in the comments.)
The background color and image parameters are removed from
StWidget's draw_background() method since they were not used
for StButton (the only current user) and the encapsulation
break that they presented caused some minor problems.
Add a test case for borders, and also use borders to style
the buttons in the 'inline-style' test case.
https://bugzilla.gnome.org/show_bug.cgi?id=595993
Add support for passing an inline-style string when creating a
StThemeNode.
Hook this up to a new 'style' property of StWidget.
Add a test case that demonstrates using this to update font sizes
on the fly.
https://bugzilla.gnome.org/show_bug.cgi?id=595991
