Changed default task time to 30mins bug 1032354
Allow for multiple urls in BROWSERID_AUDIENCE

This is to support https://oneanddone.allizom.org in addition to https://oneanddone.paas.allizom.org
Merge pull request #169 from rbillings/estimatedtime

Changed default task time to 30mins bug 1032354
Bug 1048353 - One time tasks need expiration date

Add management command and model method to close expired onetime attempts
Address review comments

Reduce size of close_expired_onetime_attempts using update()
Use a setting for TASK_ATTEMPT_EXPIRATION_DURATION
Use a create_batch and a mock datetime for test_close_expired_onetime_attempts