Replace the ZXing Java implementation with the C++ fork.
The C++ fork is faster, actively maintained and supports the MicroQR
Code barcode format.
The original Java implementation is in "Maintenance Mode Only",
what means that no new features or barcodes will be accepted.
Because the C++ fork is much faster, we can now drop RenderScript
which has been deprecated by Google anyway. Also, this removes a lot
of complications. RenderScript was never very robust.
