Updates for CSV downloads: Header letter casing unification & add column headers for edge downloads

[LibbyUX]

@katyb requests:

• CSV files downloaded from the CDE have headers with unified letter casing.
• Edge CSV file downloads have a header (with unified letter casing).

This is ready for development now and may be implemented in the CDE immediately.

Node CSV header columns in question:

Node CSV download with unified letter casing:

Edge downloads without a header:

Notes

• These two updates were initially requested on Create Vis App MVP2 #579, but it evolved into a different feature.
• This was identified as the priority 1 feature for the CDE paper by @J-Yash today, see CDE Y3 feature requests #489
• Regarding the edge downloads: I know this download is for embedding the application. Let me know if we need to break this up into two appropriately placed buttons: a "vanity" button (for lack of a better term at the moment) for edges CSVs with a header and another for edge downloads without a header for embedding the app.

[LibbyUX]

@axdanbol & I collaborate:

• Ignore casing when loading data. Link headers are optional
• Cell CSV headers: X, Y, Cell Type, [Z, Cell Ontology ID]
• Link CSV headers: TBD, I am sending an email on this now.

[LibbyUX]

@axdanbol, @bherr2 - per @J-Yash and for tracking here:

The column names/order Cell ID, X1, Y1, Z1, X2, Y2, Z2 is finalized.