Change segment editor button layout

[lassoan (Andras Lasso)]

Thanks to all the efforts of @jamesobutler, the new Segment Editor layout is now ready - see more information (and provide any feedback and suggestions) in this topic:

New Segment Editor layout - vertical effect toolbar

Thanks to all the development efforts of @jamesobutler and feedback from the community, the new, more space-efficient Segment Editor user interface is now ready (available in latest Slicer Preview Release). The main difference is that the effect toolbar is vertical, with fixed number of columns and without icon labels. This layout makes it easier to remember where to find an effect (because the same effect always appears at the same place), and the space is used more efficiently (there is less n…