Make StIcon compile and work in St.
Changes:
* ::icon-type and st_icon_set_icon_type are added to allow
specifying SYMBOLIC/FULLCOLOR for an icon.
* Ability to set the icon name from the theme is removed; it
wouldn't easily fit into our framework and two levels of
abstraction between code and image doesn't seem that useful.
* size CSS property is renamed from x-st-icon-size to icon-size
to correspond to what we are doing elsewhere.
* CSS and property based icon sizing are cleanly layered - if
you set the icon-size property, the CSS size is ignored.
* Add a simple JS test of StIcon.
https://bugzilla.gnome.org/show_bug.cgi?id=633865
The ability to set a "content image" on an icon relies on the ability
to have custom theme properties of a "border image" (9-slice) type.
We don't have this, and the capability of a bordered image specified
by the theme can be achieved more naturally with standard CSS facilities.
https://bugzilla.gnome.org/show_bug.cgi?id=633865
