Switch from qrencode to qrcode
Imported from bugseverywhere, created on 2013-12-07
we currently use the qrencode library to generate qrcodes. that library is pretty simple and wraps around the C qrencode library, but we have had problems with it before:
qrcode is a pure-python library that also installs a
qr command that can be used to test the library standalone. furthermore, it seems to be a little better maintained.
porting should be trivial, but we should check if both libraries are as well supported everywhere first.