stream acquisition: fix problem with cancelling sync sem/ccd

changing the state to RUNNING can only be done after the whole acquisition is over.
Otherwise, the previous acquisition might think it's still running if delayed in the waits.
gui: adapt pixel size automatically when magnification changes in sparc acquisition

this allows to keep the ROI at the same place and with the same repetition.
config: put correct default value in comments

speed_base default value is 0.03 m/s, not 30m/s (an old mistake)
gui: use fitViewToNextImage by default

this replaces the default that was to set the MPP to the first image.
In almost all cases we want the whole canvas to fit the view.