Implement worker queue via localStorage

[jefflunt]

Basically, check to see if the browser supports web Workers. If they do:

• Store things in localStorage
• Have a worker periodically check for new jobs, and submit them as necessary. See http://en.wikipedia.org/wiki/Web_worker#Support
• Here is a way to get all the keys in localStorage: http://stackoverflow.com/questions/8419354/get-html5-localstorage-keys
• If you use a common naming scheme (such as "job.[some unique value]" then you can submit jobs to the worker, and have them tried and retried over time.

To avoid potential threading problems:

• ONLY the page can add jobs to the queue
• ONLY the worker can remove the jobs, and only when a success status code is received from the server
• NEVER should the page care about what jobs are in the queue, or every true to read them back, or store any other temporary list of them.