An assert caused a crash when GrayDynamicsParams was set to the same
value twice.

Some assert( layerStack->GetCurrent()!=NULL ) have been replace because
GetCurrent() of a layerStack can be null if no image is open.

And those functions can be called with keyboard shortcuts.

This projection bar widget is used to edit the selected
projection zoom level.

This reverts commit 9bd55905.

BUG: maximum train and validation sizes were not correctly handled
(ac574321)

BUG: fix TrainImagesClassifier when bm=0.
(2a3cce86)