Various changes to GenericImageReader and the DataContainerInspectorWidgted to get loading arbitrary images into the DataContainer running.

Refactoring AbstractProcessor::process() for clearer semantics and better and more uniform handling of invalidation levels:
 * AbstractProcessor::process() now calls updateShader(), updateProperties() and/or updateResult() with respect to the current invalidation level
 * each processor shall no longer override process() but the updateXYZ() methods, at minimum updateResult()
 * AbstractProcessor::process() takes care of (un)locking the processor itself (no need to do this from the outside anymore)

Further implicit changes:
 * Removed redundant HasPropertyCollection::updateProperties()

Loading can be done with genericImageReader, however, assertion fails for sliders. thread ownership issues

Loading can be done with genericImageReader, however, assertion fails for sliders. thread ownership issues