[#25] Add description field to CSV import/export

The spreadsheet controller now supports a "description" column. This is
optional to support the files created in previous versions.
If the description field is empty it's assumed that the current value
(if any) needs to be deleted. Descriptions have the same unicode checks
as titles.
[#25] Ignore description if not there
Merge branch 'master' into 25-description-in-csv
Merge branch '25-description-in-csv'