Don't update hash, imagery_used when changing background in walkthrough (closes #3936)
Don't update hash, imagery_used when changing background in walkthrough
(closes #3936)

ngageoint/hootenanny-ui,ngageoint/hootenanny-ui,AndreasHae/iD,kartta-labs/iD,morray/iD,mapmeld/iD,1ec5/iD,kartta-labs/iD,digidem/iD,mapmeld/iD,digidem/iD,ngageoint/hootenanny-ui,openstreetmap/iD,1ec5/iD,AndreasHae/iD,morray/iD,bagage/iD,AndreasHae/iD,mapmeld/iD,bagage/iD,openstreetmap/iD,1ec5/iD,bagage/iD,openstreetmap/iD,kartta-labs/iD