added themes support for party modes

Output/PartyModes/Challenge/Theme.xml

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="utf-8"?>
+<root>
+  <ThemeSystemVersion>5</ThemeSystemVersion>
+  <Info>
+    <Name>Ambient</Name>
+    <Author>brunzel</Author>
+    <SkinFolder>Textures</SkinFolder>
+    <ThemeVersionMajor>0</ThemeVersionMajor>
+    <ThemeVersionMinor>1</ThemeVersionMinor>
+  </Info>
+</root>