Allow to set the large window padding mode on the ASIC

[lucabaldini]

We've always used the 10-pixel padding when reading out the ASIC, but in principle we can set a bit in the configuration register to set the padding to 20.

[lucabaldini]

I've made most of the necessary modifications from the DAQ standpoint, namely:

• we have a widget in the GUI (disabled at the moment) to select the padding mode (small or large);
• the pDetectorConfiguration class has been extended with the new field;
• there's some code (currently commented out) in the pXpolFpga class to set the appropriate bit in the configuration register.

The first attempt at using this functionality ended up in flame---the bit does something, but it's clear that we're not reading out the events as we should. Some basic phenomenology:

• the windows are ~twice as large (and rightfully so) in one direction---either x or y, apparently randomly;
• the aspect ratio of the window tend to be ~0.5
• the events seem mostly noise-like on the monitor, although occasionally we see decent events---mainly on the border.

We need to look at this in details. We currently don't know if it's a problem with the DAQ, the firmware or the ASIC.