Fixes https://gitlab.com/kicad/code/kicad/issues/4306
ADDED: create/edit/delete nets in PCBnew Net Inspector ADDED: update from PCB now allows updating of changed nets Fixes https://gitlab.com/kicad/code/kicad/issues/1996
ADDED: Back annotation algorithm, eeschema back annotation dialog CHANGED: added some minor helper methods to SCH_REFERENCE_LIST and SCH_REFERENCE, split SCH_REFERENCE_LIST::CheckAnnotation on 2 parts to reuse code