Don't activate EventIcons after touch long press

Steps to reproduce:

1.  Long press activity icon on homeview
Expcected:  Palette invokes, icon not activated
Actual:     Palette invokes, icon also activated, activity launched

This was because the "activate" signal was emitted before the
palette invoker got it's signal, meaning the palette invoker couldn't
scilence the event.

src/sugar3/graphics/icon.py

@@ -576,6 +576,10 @@ class EventIcon(Gtk.EventBox):
                         Gdk.EventMask.TOUCH_MASK |
                         Gdk.EventMask.BUTTON_RELEASE_MASK)
         self.connect('button-release-event', self.__button_release_event_cb)
+        # Connect after the default so that the palette can silence events
+        # for example, after a touch palette invocation
+        self.connect_after('button-release-event',
+                           self.__button_release_event_cb)
         for key, value in kwargs.iteritems():
             self.set_property(key, value)