Slight improvements to tests/factories
Support for recurring pledges

Pledges can now be recurring, in which case they are autorenewed when
they are ended. This sends a somewhat different email to the donor.
Take advantage of pledge_summary

Use this and feedback_for in the PledgeHelper to simplify and consistify
some code
Add radio buttons for recurring bit on pledges

Users can now choose "this month" vs. "every month" when creating or
updating a pledge, in order to set the recurring? bit.

Also DRY up the forms with a partial.