Page size problem

[aditsu]

Nice little web application, but the page size seems to be hardcoded in swis.py, to 211*297 mm. That doesn't really work with my scanner, and I get the error:
scanimage: setting of option --br-y failed (Invalid argument)

scanimage -A outputs (among other things):

    -l 0..215.9mm [0]
        Top-left x position of scan area.
    -t 0..296.926mm [0]
        Top-left y position of scan area.
    -x 0..215.9mm [215.9]
        Width of scan-area.
    -y 0..296.926mm [296.926]
        Height of scan-area.

Changing the numbers in swis.py fixes the problem, but that's not ideal. Here are 3 possible solutions:

1. make the page size configurable via the web interface and/or a config file
2. autodetect the available scan area from scanimage
3. do a full size scan by default by not passing any -x and -y values

[rsusik]

Thanks, it's weird to me as it should be 210 x 297. You can drop a PR if you wish to contribute to the project.