rename basedata_name sv_obj_helper Operator

Created by: zeffii

addresses #2825 and #3391

allowing inplace-renaming basedata_name a feature which was never implemented fully

• first implement a canonical Operator which handles BMviewer as generically as possible.
• handle name collisions (other nodes with same basedata_name breaks the abstraction, it must not be allowed)
• offer to auto rename the datablock too
• add operator to UI drawing func of sv_obj
• gradually make sure all sv_obj_helper heirs are handled individually
  • bmesh viewer
  • curve viewer
  • polyline viewer
  • .... etc
• experiment with changing the default update function of the basedata_name StringProperty, so that the button is not needed and the update function instead triggers the appropriate code to handle the type of viewer node.