Identify duplicate cells between secondary datasets in CxG

[andreasbueckle]

This is only an issue for the collection b1a879f6-5638-48d3-8f64-f6592c1b1561

• @axdanbol investigates the extent of this issue
• When this happens, it an error in the cell type annotation tools (all 3).
• Need to evaluate new cell type counts after run v0.6.

[axdanbol]

Duplicate cells between secondary datasets are now filtered out during the download phase.