Switch from St.TextureCache.load_named_icon() to using St.Icon for named
icons. Along with the advantage of getting colorization right for symbolic
icons, this allows moving some icon sizes into the CSS.
In the CSS, the system status icon size is changed to be 1em (=16px for the
default font size), at the request of the artists. See bug 613448.
https://bugzilla.gnome.org/show_bug.cgi?id=633865
Each menu is a focus manager group, but there is also some explicit
focus handling between non-hierarchically-related widgets. Eg, to move
between menus, or from a menubutton into its menu.
https://bugzilla.gnome.org/show_bug.cgi?id=621671
Icons can be loaded as St.Icon.SYMBOLIC, FULLCOLOR, APPLICATION or
DOCUMENT. The first will look for a symbolic equivalent, the second
looks for a full-color version (and does fallback, eg, from
"drive-harddisk-usb" to "drive-harddisk"). APPLICATION and DOCUMENT do
full-color icons without fallback (as specified by the icon spec).
And update various callers to use the right flags.
Based on a patch from Matt Novenstern.
https://bugzilla.gnome.org/show_bug.cgi?id=621311
Solved by splitting the base class (PanelMenuButton) in a separate
module, ui.panelMenu, which is meant to hold also other reusable
button classes.
https://bugzilla.gnome.org/show_bug.cgi?id=621705
