Layer Display: add menu items and shortcuts for new actions

gtk2_ardour/ardour.keys.in

@@ -305,6 +305,9 @@ This mode provides many different operations on both regions and control points,
 @gedt|Common/start-loop-range|<@SECONDARY@>comma|set the start of the Loop range
 @gedt|Common/finish-loop-range|<@SECONDARY@>period|set the end of the Loop range
 
+@edit|Editor/layer-display-stacked|<@TERTIARY@>less|Display Region Layers: Stacked
+@edit|Editor/layer-display-overlaid|<@TERTIARY@>greater|Display Region Layers: Overlaid
+@edit|Editor/show-plist-selector|<@TERTIARY@>question|show-plist-selector
 @gmark|Common/alternate-add-location-from-playhead|KP_Enter|add mark at playhead
 @gmark|Common/alternate-remove-location-from-playhead|<@PRIMARY@>KP_Enter|add mark at playhead
 @wvis|Transport/focus-on-clock|KP_Divide|focus on main clock

gtk2_ardour/ardour.menus.in

@@ -437,7 +437,10 @@
         <menuitem action='track-height-small'/>
       </menu>
       <separator/>
-        <menuitem action='toggle-layer-display'/>
+      <menu name='LayerDisplay' action = 'LayerDisplay'>
+        <menuitem action='layer-display-stacked'/>
+        <menuitem action='layer-display-overlaid'/>
+      </menu>
       <separator/>
       <menuitem action='toggle-track-active'/>
       <menuitem action='remove-track'/>
@@ -449,6 +452,10 @@
       <menuitem action='ToggleMaximalMixer'/>
 
       <separator/>
+      <menu name='LayerDisplay' action = 'LayerDisplay'>
+        <menuitem action='layer-display-stacked'/>
+        <menuitem action='layer-display-overlaid'/>
+      </menu>
 
       <menu action="AutomationMenu">
         <menuitem action="toggle-all-existing-automation"/>
@@ -456,8 +463,6 @@
 
       <separator/>
 
-      <menuitem action="toggle-layer-display"/>
-      
       <menu action="PrimaryClockMenu">
         <menuitem action='focus-on-clock'/>
         <menuitem action="primary-clock-timecode"/>