Clean up MutterPlugin effect interface

The current effect API passes an unnecessary list of windows to
switch_workspace() and forces a window to be passed in when killing
the switch_workspace() effect.

We can simplify the interface to correspond more closely to how
it is actually used and fix these problems:

Remove the actors parameter to plugin->switch_workspace
Remove the events parameter to plugin->kill_effect and rename it to kill_window_effects
Add plugin->kill_switch_workspace

Remove mutter_plugin_manager_kill_effect
Add mutter_plugin_manager_kill_window_effects
Add mutter_plugin_manager_kill_switch_workspace

Remove mutter_plugin_effect_completed
Add mutter_plugin_[minimize/map/destroy/maximize/unmaximize]_completed
https://bugzilla.gnome.org/show_bug.cgi?id=621082

src/compositor/compositor.c

@@ -790,7 +790,6 @@ meta_compositor_switch_workspace (MetaCompositor     *compositor,
 
   if (!info->plugin_mgr ||
       !mutter_plugin_manager_switch_workspace (info->plugin_mgr,
-					       (const GList **)&info->windows,
 					       from_indx,
 					       to_indx,
 					       direction))