- adds git submodule libqrencode from
https://github.com/fukuchi/libqrencode.git
- adds button to show/hide the qrcode.
- updates CMakeList.txt to use libqrencode.
- updates the client to show the qrcode.

Change-Id: I7255c93d67a4c884d17afd5e517e0c3345d9b269
Tuleap: #548