When implementing bug 765359, it appears that Geary is doing too much
work to load icons. Simplify it a bit.
* src/client/components/icon-factory.vala (IconFactory): Don't bother
loading an application icon, it's easier and works better to just use
an icon name where needed. Don't bother adding all of the icons/*x*
directories to the icon theme search path, just make the icon's
directory hierarchy follow the XDG/hicolor spec and add the base
directory. Remove now-redundant code.
* src/client/application/geary-controller.vala: Set the default icon name
for all geary windows.
(GearyController:on_about()): Set the name for the icon in the About
dialog.
* src/client/components/main-window.vala (ApplicationWindow): Don't
bother loading icons for the window, just use the new default.
* src/client/notification/libnotify.vala: Don't bother passing the
application icon through for error notifications, an icon name has
already been set.
* icons/*x*/geary.png: Move to a new directory hierarchy that follows the
hicolor spec.
* icons/CMakeLists.txt: Updated to use new paths to the icons.
