Importer: Make group name sticky

[tbar0970]

When you use Admin > Import, you have to put the imported persons into a group.
You can type a group name to create a new group
but if there's an error with the import data (there often is), then you have to type the name in again for the second (and third) go.
It would be good to pre-populate that field if there is a group name in the request.

[tbar0970]

also the selection of group to put people in