Bundlebuilder: Use installed icon path in .desktop file

Previously, the bundle builder referenced the icon path in the
source directory - which was obviously not installed in the package.

src/sugar3/activity/bundlebuilder.py

@@ -333,7 +333,8 @@ class Installer(Packager):
         cp.set(section, 'Terminal', 'false')
         cp.set(section, 'Type', 'Application')
         cp.set(section, 'Categories', 'Education;')
-        cp.set(section, 'Icon', self.config.bundle.get_icon())
+        cp.set(section, 'Icon', os.path.join(
+            activity_path, 'activity', self.config.bundle.get_icon_filename()))
         cp.set(section, 'Exec', self.config.bundle.get_command())
         cp.set(section, 'Path', activity_path)  # Path == CWD for running
 

src/sugar3/bundle/activitybundle.py

@@ -286,6 +286,10 @@ class ActivityBundle(Bundle):
             os.close(temp_file)
             return temp_file_path
 
+    def get_icon_filename(self):
+        '''Get the icon file name'''
+        return self._icon + '.svg'
+
     def get_activity_version(self):
         """Get the activity version"""
         return self._activity_version