reuse categories

To prevent duplicate category IDs, we currently timestamp the cat ID. It turns out that the dash never forgets categories, so this is wasteful.

Also, this approach will not work well with upcoming changes to the dash in which category IDs are expected to be more persistent (so that on user entered searches the dash can modify the qml model and the categories that were present will be reused appropriately).

Therefore, we need a better approach to category IDs, probably as follows:
instead of timestamping the cat id, use tokens like:
TYPE:FULLYQUALIFIEDCHILDSCOPEID

All agg scopes will need to be rebased using this before the planned changed to the dash described above.