Smooth out take_over tests
Smooth out take_over tests

Change from `alice_participant` and `alice` to `alice` and
`alice_twitter`. Makes it easier to reason about participants vs.
accounts elsewhere if we use this nomenclature.

gratipay/gratipay.com,gratipay/gratipay.com,eXcomm/gratipay.com,gratipay/gratipay.com,mccolgst/www.gittip.com,eXcomm/gratipay.com,mccolgst/www.gittip.com,studio666/gratipay.com,mccolgst/www.gittip.com,eXcomm/gratipay.com,gratipay/gratipay.com,studio666/gratipay.com,studio666/gratipay.com,mccolgst/www.gittip.com,eXcomm/gratipay.com,studio666/gratipay.com