ShellApp: Change activation API

Since almost all of the callers of shell_app_activate were using the
default workspace (by passing -1), remove that parameter.

Add a new shell_app_activate_full() API which takes a workspace as
well as a timestamp; previously we might have been ignoring event
timestamps from elsewhere.

https://bugzilla.gnome.org/show_bug.cgi?id=648149

js/ui/endSessionDialog.js

@@ -173,7 +173,7 @@ ListItem.prototype = {
 
     _onClicked: function() {
         this.emit('activate');
-        this._app.activate(-1);
+        this._app.activate();
     }
 };
 Signals.addSignalMethods(ListItem.prototype);