Importer: ability to set note subject, status and assignee

[tbar0970]

Currently the importer allows you to include a "note" column which will be saved as a person note with subject "import note". It would be useful to be able to set the subject of the note to something else and to set a particular status and assignee for the note (eg requires action by Joe Bloggs). Applying a single value for these fields across the whole import would be fine, although per-row values might be useful.