Add rename to output comboboxes

See Issue #13882
Drastically improve the node color change performance

The volume node is observe by the setupMergeLabel() function that is
called upon the ModifiedEvent. Without the StartModify() and EndModify(),
each time the node was modified the function was called, slowing down the
process a lot.
Now the modified event is only called one at the EndModify().

See Issue #13882
Uniform GUI

Use same casing for the labels throughout the module, following the slicer
convention.
Also Using "WordWrap" in the help label.
Finally, moving the GoTo buttons next to the apply buttons.

See Issue #13882
Delete First/Last workflow buttons

There were not used anyway. Also leaving an empty space for the
next/previous button when at the last/first page.

See Issue #13882
GUI Tweaks

Add a), b) c) to collapsible groupbox titles.
Make the pose body output combo box visible in advanced mode.

See Issue #13882