don't archive participant when closing account

but set claimed_time to NULL
make sure that balance and tips have been dealt with
reset session_token and session_expires when closing account
Here's a failing test for settings attributes

Since we're bothering to set attributes we may as well set all of them,
no?
Fix for settings additional attributes
Merge pull request #2486 from gittip/close-dont-archive

Don't archive participant when closing account