CebraEM: Table in MoBIE project misses anchors

[jhennies]

When viewing a mask in MoBIE that has multiple objects, it would be nice to be able to navigate to each object using the table entries.
Currently all objects are anchored to (0, 0, 0).

This would require parsing all objects at project initialization and determining their center point within the dataset (could be done on a lower resolution level)