Scan settings are now remembered
All settings on the "capture" pane, except "scan capture" are now remembered in local storage. "scan capture" changes the "scan" button from a snapshot to a long scan - so I think it's reasonable to require the operator to explicitly select it before starting the scan. This should avoid people clicking the button and unexpectedly getting a scan instead of a snapshot.
I've also set the interface to auto-expand the scan pane if scanCapture is selected, again to try to avoid confusion. I did this before deciding scanCapture shouldn't be remembered, but I think it's reasonable to leave it there as it will be useful in any situation where the capture pane has its values changed programmatically - e.g. if we introduce preset settings.
Closes #216 (closed)