add api for adding/removing endpoints
ping endpoints on version updates
use cas instead of set to prevent write collisions
add a retry-loop for adding and deleting endpoints
refactor retry logic so new casid is captured
Merge pull request #67 from mozilla/push-service

Store push server endpoints and ping them on version updates
use firefox.persona.org as the persona verifier
Merge pull request #72 from mozilla/firefoxos_verifier

use firefox.persona.org as the persona verifier
fixes #68: skip testing of endpoints on remote servers, since we cannot reliably detect interactions with the push server it is using
Merge pull request #73 from mozilla/skip_remote_endpoint_testing

fixes #68: skip testing of endpoints on remote servers, since we cannot ...