Made approval billing reports not select rejected approval tasks

Added tasks.complete_approved/complete_rejected.  I keep writing these
methods in the unittests, so we might as well add them to the Task
class.  Made Task.complete() return the review task for rejected
approval tasks.
Remove subtitler/reviewer replace with approver for billing reports

Janet points out that we'll have the subtitler/reviewer in the report
to pay people, so we don't need it here.

Fixed code that calculates names to use unicode() instead of
full_name.  This should result in "<first_name> <last_name>".