Add feature that allows user to set the language

Implemented #260.

I added some compile options so that Java 7 is supported. This will require the developers to rebuild the project and also to uninstall - install the Antox app on the devices they are debugging.
Java 7 is required in order to the switch on Strings can be made.

The set of the language works, but the activity has to be restarted. That's the only way the configurations can be changed.