ENH: Added "Enable developer mode" option to ExtensionWizard

Developer mode is quite important for scripted module developers, as
it enables showing of the "Reload and test" section in scripted module
GUI.

To make sure developers not forget to enable developer mode, added a
checkbox to enable developer mode to the scripted module auto-load dialog.
The checkbox is checked by default and it is only shown if developer mode
is not enabled already.

From: Andras Lasso <lasso@queensu.ca>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23779 3bd1e089-480b-0410-8dfb-8563597acbee