Set category after import for detailed guide

Allow detailed guide to be imported without a mainstream category. It is
required to move into the draft state however.
Work around CSV cell size restrictions for body

Some spreadsheet programs have errors when exporting CSVs with very long
cell sizes (>32k). We have occasionally hit this problem with body
fields.

This change allows multiple numbered body fields which will be
concatenated.
Fix heading validation argument error

oops, sorry