ENH: Subject hierarchy nodes not auto-created by default

Subject hierarchy auto-creation has caused problems in other modules (like Models, see referred ticket), and some users won't use subject hierarchy, so the supported data nodes are not added to the hierarchy automatically.
Now when the user enters subject hierarchy, and there are supported nodes (i.e. there is an SH plugin that can handle the node) in the scene, a question pops up whether the user wants to create subject hierarchy. If they say no, the hierarchy remains empty and unusable, if they choose yes, then the hierarchy is created once, if they choose yes to all, then a setting is saved and auto-creation is turned on, which means every added node that is supported by SH is automatically added. The users who use subject hierarchy often, should choose this option.

Related to 0003911

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23817 3bd1e089-480b-0410-8dfb-8563597acbee