begin.html :
tweaked to hopefully always display the mask if the module is not enabled

OpenCyto.css :
modified to include simple-panel-header class, which has white background, no border etc
removed checkBoxWithLeftMargin class (replaced it with config options for the JS initializer)

OpenCytoPreprocessing :
tweaked so that if the SampleGroups were not loaded for some reason, selecting an item in XML combo tries to fetch the sample groups choices again
replaced list of containers with obscure structure with a list of panels, applying the simple-panel-header class to their panels