Tracked handler streamline

Created by: zeffii

backend cleanup of features.

• introduces sv_execute(self, context, node) to Operators that use mixin SvGenericNodeLocator
• if you still want to write the full def execute(self, context) you can, i've left some of the more elaborate execute implementations unchanged.
• in sv_execute you can always return early. Using return will always result in return {"FINISHED"},
  • you can return {"CANCELLED"} explicitely if you want. (or any other of the accepted Set values

a typical SvGenericNodeLocator operator would change from

    ...

    def execute(self, context):
        """
        passes the operator's 'self' too to allow calling self.report()
        """
        node = self.get_node(context)
        if node:
            node.get_objects_from_scene(self)
            return {'FINISHED'}

        return {'CANCELLED'}

to this

    def sv_execute(self, context, node):
        """
        passes the operator's 'self' too to allow calling self.report()
        """
        node.get_objects_from_scene(self)

as you can see, the node locating is entirely taken care of.