Android keyboard input type fix

On some devices (as my HTC One X plus running Android 4.2.2), the default keyboard that is used in libGDX always uses the input type that was last used. This means when you run some application that uses a digit-only keyboard, then exit that application and start the libGDX application directly, a digit-only keyboard will show up when trying to write into an InputField.
This fix uses an old way to handle keyboard input that was already built into libGDX, but never used. It just uses a hidden TextView element with the input type TEXT. The key inputs are then routed to the AndroidInput as usual.