Grid view for ufo

Addition of a coloured 8x8m lattice box around the UFO, switched on/off using
Ctrl+G.  This is to aid configuration of multi-monitor displays.

Aircraft/ufo/Models/ufo.xml

@@ -17,6 +17,19 @@
   </condition>
  </animation>
 
+ <animation>
+  <type>select</type>
+  <condition>
+   <property>/sim/model/display-grid</property>
+  </condition>
+  <object-name>GridBottom</object-name>
+  <object-name>GridFront</object-name>
+  <object-name>GridPort</object-name>
+  <object-name>GridRear</object-name>
+  <object-name>GridStarboard</object-name>
+  <object-name>GridTop</object-name>
+ </animation>
+
  <animation>
   <type>blend</type>
   <object-name>body</object-name>

Aircraft/ufo/ufo-set.xml

@@ -223,6 +223,10 @@
 				<name>=</name>
 				<desc>open/close cursor dialog</desc>
 			</key>
+			<key>
+				<name>Ctrl + G</name>
+				<desc>Show/hide 8x8x8m box grid around ufo for screen alignment</desc>
+			</key>
 
 			<line>Pre-select initial model (path relative to $FG_ROOT):</line>
 			<line>&#32;&#32;&#45;&#45;prop:cursor=Model/path.xml</line>
@@ -255,15 +259,9 @@
 				<name>Ctrl-G</name>
 				<desc>Gear Up.</desc>
 				<binding>
-					<command>nasal</command>
+					<command>property-toggle</command>
-					<script>controls.gearDown(-1)</script>
+					<property>/sim/model/display-grid</property>
 				</binding>
-				<mod-up>
-					<binding>
-						<command>nasal</command>
-						<script>controls.gearDown(0)</script>
-					</binding>
-				</mod-up>
 			</key>
 
 			<key n="61">