Add new Android voice translator sample app

This adds a simple voice translator Android app that uses
the JNI bindings to the PGF C runtime.

Caveats:

- Since the C runtime doesn't compile for Android right now,
  I've bundled an old copy, along with its Java bindings.
  That should be removed once the C runtime compiels for Android
  again.

- Adding an automated build would be nice.

- Replacing the grammar requires editing a Java file, that should 
  really be more dynamic.

src/ui/android/res/values/strings.xml

@@ -1,8 +1,9 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
 
-    <string name="app_name">GFTranslator</string>
-    <string name="action_settings">Settings</string>
-    <string name="hello_world">Hello world!</string>
+    <string name="app_name">GF Translator</string>
+
+    <string name="microphone">Microphone</string>
+    <string name="switch_languages">Switch languages</string>
 
 </resources>