(no ticket) Add manage.py import_participants

which imports participants from a simple one-login-per-line text file.

Change-Id: I8ece34908960f03a7e35daed5d29280e8ad0a768
(no ticket) Add manage.py import_users

Creates user accounts from a CSV file.

Change-Id: I3d3f346502ec7bff7d92817db0e522a2e05a75b6
Merge changes I3d3f3465,I8ece3490

* changes:
  (no ticket) Add manage.py import_users
  (no ticket) Add manage.py import_participants