Common object-handler mixin + operator (callback)

Закрыто nikitronn запросил слияние obj_helper_class в master

Created by: zeffii

Tick doesn't mean it works. or is tested, just means I added the bulk of the required code to the proposed mixin.

  • getting children of the node (objs = )
  • generating truely unique object / data names using a sverchok dict, rather than scene tests
  • setting materials
  • generating material (one material for all...)
  • cleanup orphan objects
  • hide / hide_select / hide_render / select operations.
  • include layer handling
  • reuse UI icon code ( kinda klunky at the moment...)
  • add grouping code (no ungroup?)
  • add parenting code (no unparent?)
  • fix merging in BMVmk3
  • add nodetree/nodename to callback operator (else the node UI must be active/selected first )
  • migrate all viz nodes to name their "objects" using some form of this line. 
    data_name = node.basedata_name + '.' + str("%04d" % obj_index)
  • include per object material passing. (material name per object)
  • easy auto update the node switches for hide/select/hide_select https://github.com/nortikin/sverchok/issues/1930
  • convert PolylineViewerMK2 to use sv_obj_helper
  • convert BMeshViewerMK3 to use sv_obj_helper
  • convert CurvesViewerMK2 to use sv_obj_helper
  • convert CurvesViewer2DMK2 to use sv_obj_helper
  • convert SkinViewerMK2 to use sv_obj_helper
  • convert TypographyViewerMK2 to use sv_obj_helper
  • convert MetaballViewer(MK2?) to use sv_obj_helper