CamReader.py pep8-ifyied
setexposure.php

We don't need to load an image for just setting the exposure, thus stripped down globaldiagnostix.php to setexposure.php, which we can use with a urllib.urlretrieve-call
CamReader.py now correctly sets the exposure time

- New option Exposure, since we can use it in any of the three modes
- Put the exposure-setting logic into a function, which we can call where we need it. The logic was based on a 'wget' call, but we can do it in pure python much more elegantly by using urllib.urlretrieve
GPIO_output now reads PIN from commandline

It's actually a bit more clever if we read the PIN to set from the command-line, so we can quickly set different PINs. Tomorrow I want to try to trigger the x-ray source with setting an IO of the Raspberry Pi to high...