Add enable-vr and disable-vr options

Add command line options for enabling and disabling VR. These are placed
at the end of the features section for want of a better place.

Translations/default/options.xml

@@ -71,6 +71,8 @@
 	<enable-anti-alias-hud-desc>Enable anti-aliased HUD</enable-anti-alias-hud-desc>
 	<disable-hud-3d-desc>Disable 3D HUD</disable-hud-3d-desc>
 	<enable-hud-3d-desc>Enable 3D HUD</enable-hud-3d-desc>
+	<disable-vr-desc>Disable VR</disable-vr-desc>
+	<enable-vr-desc>Enable VR</enable-vr-desc>
 
 	<!-- Aircraft options -->
 	<aircraft-options>Aircraft</aircraft-options>

Translations/en_US/FlightGear-nonQt.xlf

@@ -757,6 +757,10 @@
           <source>Disable textures</source>
           <target />
         </trans-unit>
+        <trans-unit id="options/disable-vr-desc:" translate="yes" approved="no">
+          <source>Disable VR</source>
+          <target />
+        </trans-unit>
         <trans-unit id="options/disable-wireframe-desc:0" translate="yes" approved="no">
           <source>Disable wireframe drawing mode</source>
           <target />
@@ -889,6 +893,10 @@
           <source>Enable textures</source>
           <target />
         </trans-unit>
+        <trans-unit id="options/enable-vr-desc:" translate="yes" approved="no">
+          <source>Enable VR</source>
+          <target />
+        </trans-unit>
         <trans-unit id="options/enable-wireframe-desc:0" translate="yes" approved="no">
           <source>Enable wireframe drawing mode</source>
           <target />

options.xml

@@ -319,6 +319,16 @@
     <description>enable-clock-freeze-desc</description>
    </option>
 
+   <option>
+    <name>disable-vr</name>
+    <description>disable-vr-desc</description>
+   </option>
+
+   <option>
+    <name>enable-vr</name>
+    <description>enable-vr-desc</description>
+   </option>
+
    <option>
     <name>failure</name>
     <arg>{pitot|static|vacuum|electrical}</arg>