add build script for mobile version

mobile/HACKING.md

@@ -22,3 +22,7 @@ Building the APK
   ```export ANDROID_HOME=/path/to/android_sdk```
   and build the project with ant:
   `ant debug`
+- You can use `build_mobile.js`, too, which builds IITC, compresses
+  it and uses ant to build a release APK of IITCM. It requires that
+  you have Python and uglifyjs installed. You need to set the
+  `ANDROID_HOME`, like explained above.

mobile/build_mobile.js

@@ -0,0 +1,12 @@
+#!/bin/sh
+
+set -e
+
+cd `dirname "$0"`
+cd ..
+./build.py
+compressed="$(uglifyjs iitc-debug.user.js)"
+echo "${compressed}" > "iitc-debug.user.js"
+
+cd mobile
+ant release