Fix detection of edit event when adding a new assignee
Fix detection of edit event when adding a new assignee

When user's relatonship with object is first created, relationship
attributes are marked as unchanged. Because this happens on POST
event, we detech which method was used and interpet that change
as editable event that should trigger status change.

NejcZupec/ggrc-core,plamut/ggrc-core,josthkko/ggrc-core,AleksNeStu/ggrc-core,josthkko/ggrc-core,andrei-karalionak/ggrc-core,AleksNeStu/ggrc-core,edofic/ggrc-core,VinnieJohns/ggrc-core,plamut/ggrc-core,j0gurt/ggrc-core,selahssea/ggrc-core,plamut/ggrc-core,VinnieJohns/ggrc-core,j0gurt/ggrc-core,AleksNeStu/ggrc-core,AleksNeStu/ggrc-core,edofic/ggrc-core,j0gurt/ggrc-core,edofic/ggrc-core,kr41/ggrc-core,j0gurt/ggrc-core,selahssea/ggrc-core,selahssea/ggrc-core,plamut/ggrc-core,andrei-karalionak/ggrc-core,andrei-karalionak/ggrc-core,josthkko/ggrc-core,VinnieJohns/ggrc-core,kr41/ggrc-core,NejcZupec/ggrc-core,NejcZupec/ggrc-core,VinnieJohns/ggrc-core,kr41/ggrc-core,josthkko/ggrc-core,kr41/ggrc-core,NejcZupec/ggrc-core,selahssea/ggrc-core,andrei-karalionak/ggrc-core,edofic/ggrc-core