Some prepatory work for User ATC/AI interactions.

- Renable the ATC dialog in keyboard.xml
- Add two new materials in Symbols: A unidirectional and a bidirectional arrow tape.

keyboard.xml

@@ -338,9 +338,8 @@ top down before the key bindings are parsed.
   <desc>Display a dialog relevant to the tuned in ATC service (if any)</desc>
   <binding>
     <!-- At the moment, we have no working interactive ATC, so this is
-         disabled for v2.2.0.
+         disabled for v2.2.0. -->
     <command>ATC-dialog</command>
-    -->
   </binding>
  </key>
 

materials.xml

@@ -3203,4 +3203,26 @@ Shared parameters for various materials.
   </emissive>
  </material>
 
+ <material>
+     <name>UnidirectionalTaper</name>
+     <texture>Symbols/unidirectional.png</texture>
+     <emissive>
+         <r>0.92157</r>
+         <g>0.92157</g>
+         <b>0.76471</b>
+         <a>1.0</a>
+     </emissive>
+ </material>
+
+ <material>
+     <name>BidirectionalTaper</name>
+     <texture>Symbols/bidirectional.png</texture>
+     <emissive>
+         <r>0.92157</r>
+         <g>0.92157</g>
+         <b>0.76471</b>
+         <a>1.0</a>
+     </emissive>
+ </material>
+
 </PropertyList>