Cut down on boilerplate by using the (no longer that) new helper
macros. We don't care about breaking ABI in private libraries, so
use G_DECLARE_FINAL_TYPE even where the class struct used to be
exposed in the header, except for types we inherit from ourselves
(obviously) or where the class exposes any vfuncs (where changes
could affect inheritance in extensions).
If the user clicks on the title of a trayicon's SummaryItem, forward
that click to the trayicon. Also adjust
gnome_shell_plugin_xevent_filter() so that if the trayicon takes a
grab as a result of this, we don't hide the message tray.
https://bugzilla.gnome.org/show_bug.cgi?id=630842
The actor emitted by ShellTrayManager is now ShellTrayIcon, a subclass
of ShellGtkEmbed which has several properties on it which are (or will
soon be) useful to the shell.
Part of the rearranging to use ShellTrayIcon means that we now show
the ShellEmbeddedWindow before creating its ShellGtkEmbed, which
requires a few modifications to ShellEmbeddedWindow (notably, telling
it at construct time what stage it will be drawn on, since it needs to
know that before it has a ShellGtkEmbed now).
https://bugzilla.gnome.org/show_bug.cgi?id=608869
