Enable tycho-extension

Needed as target platform doesn't have a pom and thus updateTarget
doesn't work.

Author: akurtakov

.mvn/extensions.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<extensions>
+  <extension>
+    <groupId>org.eclipse.tycho</groupId>
+    <artifactId>tycho-build</artifactId>
+    <version>4.0.12</version>
+  </extension>
+</extensions>