Identify factors that are automatically generated and can safely be deleted or re-created

[arteymix]

There is currently no way to tell if a factor was curated manually and whether it is reasonable to delete it automatically. This is problematic for the batch factor and also the cell type factor.

• add a field in the experimental factor model to indicate if it was generated automatically
• unset the flag when factors, their values or their characteristics are edited by a curator
•  backfill the IS_AUTO_GENERATED flag for common cases (e.g. batch and cell types)
• ignore manually curated batch factors when filling batch information from FASTQ headers
• do not recreate the cell type factor if it was manually curated
• clearly mark in the UI which factors Gemma considers to be auto-generated

[ppavlidis]

Gemma 2 disposition: Won't fix