Configure proguard to keep application name

A crash was reported with the following error:

java.lang.RuntimeException: Unable to instantiate application org.helllabs.android.xmp.XmpApplication: java.lang.ClassNotFoundException: org.helllabs.android.xmp.XmpApplication in loader dalvik.system.PathClassLoader[/mnt/asec/org.helllabs.android.xmp-2/pkg.apk]

Change the proguard configuration to keep application class name intact.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>