Float fields are needed to round amounts.
Also, discard empty form groups.
Also, make "hidden" the first group, so any created field gets hidden by default
(which is what we want for all listbox "editable" fields).
Also, remove overrides which seem unneeded for report appearance:
- "lines" is not used for OD* rendering
- "columns" is already the same as in original field
"editable_columns" is used in odt (and maybe in ods, unclear), but
inconsistently with its intended use... so leave it, sadly.