Orphaned space-views when resetting blueprint

[jleibs]

When resetting a space-view blueprint, such as for plots, we end up with 10 space-views in the blueprint timeline.

seems like a bunch get created on the first frame, then lost and replaced with others that have the same content.

easy to repro by running the plot example and resetting the blueprint

[jleibs]

@Wumpf wondering if this is somehow related to the new hash tracking logic