only clear nodes on topo or grouping change
only clear nodes on topo or grouping change

fixes #133

dilgerma/scope,davkal/scope,neviim/scope,davkal/scope,alban/scope,weaveworks/scope,dilgerma/scope,kinvolk/scope,tomwilkie/scope,weaveworks/scope,mbrukman/scope,barravi/scope,cgvarela/scope,dilgerma/scope,davkal/scope,cgvarela/scope,mbrukman/scope,weaveworks/scope,dilgerma/scope,neviim/scope,weaveworks/scope,paulbellamy/scope,weaveworks/scope,kinvolk/scope,philipz/scope,alban/scope,barravi/scope,tomwilkie/scope,philipz/scope,alban/scope,paulbellamy/scope,philipz/scope,cgvarela/scope,alban/scope,cgvarela/scope,barravi/scope,paulbellamy/scope,mbrukman/scope,tomwilkie/scope,barravi/scope,neviim/scope,kinvolk/scope,davkal/scope,cgvarela/scope,philipz/scope,tomwilkie/scope,dilgerma/scope,mbrukman/scope,neviim/scope,barravi/scope,weaveworks/scope,alban/scope,mbrukman/scope,tomwilkie/scope,mbrukman/scope,davkal/scope,kinvolk/scope,neviim/scope,neviim/scope,cgvarela/scope,paulbellamy/scope,paulbellamy/scope,dilgerma/scope,davkal/scope,paulbellamy/scope,tomwilkie/scope,kinvolk/scope,barravi/scope,philipz/scope,alban/scope,philipz/scope,kinvolk/scope