SignPages: Remove the scrolled window container for the QR Code

I don't know why we would want to scoll anyway. We try to display the QR
Code as large as possible.
Using the custom logic of QRCode
SignPages: Removed duplicated qr code logic

We now find all of that in the qrcode module
QRCode: Remove the data argument from the draw call
QRCode: Introduced logging
QRCode: Setting a window size in main()
QRCode: Made image_to_pixbuf a staticmethod
QRCode: Made the create_qrcode a staticmethod
QRCode: Added some documentation
QRCode: We do not need to manually call draw_qrcode

I guess because we will have at least one size request which in turns
draws the code.
Initial version of GPGQRCode, a PGP Key Barcode generator
QRCode: Made the widget a DrawingArea for proper resizing

There was a problem when maximising the application and then resizing it
back to its original size, i.e. Super+Up and then Super+Down.
The window would not go back to its size, but rather stay larger.
With this change, it works much better. Thanks benzo.
SignPages: Removed duplicate QR Code drawing logic
QRCode: Made it open a fullscreen window on click
QRCode: Closed the window on keypress

So far, it is Escape, F, or Q.  But that's a bit arbitrary and can
be amended.  In fact, any key might be an idea.