Create website-allcheck build

Summary:
This configuration is a copy of website-commit, except that it only
polls git for changes and to kick off a build every few hours rather
than every few minutes.

Test Plan: Ran website-allcheck build on jenkins.khanacademy.org

Reviewers: csilvers

Reviewed By: csilvers

Differential Revision: http://phabricator.khanacademy.org/D2460