User terms

Notes:

- due to core Profile not being a FieldAPI module, User terms needs to continue supporting this. Hence migration is optional (and one-way!)
- add an option (and a form?) to only migrate vocabularies that are on the account page?

Instructions for setting up a test environment:

- Install D7
- Enable devel, devel generate
- Enable user_terms
- Generate 0 vocabs (ie put them into the existing tags vocab), 20 terms (more than 1 vocab and you run into issues with which terms are in which vocabs)
- Generate 10 users
- Import the attached SQL file. This inserts dummy data into term_user and sets the variables that the migration plan expects to find.

Still todo:

- adapt object manipulation to use information from hook_field_schema() so values go into the right place!

This now works! :D