Support public tasks

[hannah-martinez]

Note that I define a public task as a task available to an authenticated, unauthorized user. Authenticated means they've logged in with a Google account, unauthorized means that an admin user has not yet moved this user to the AuthorizedUsers group in the Django console.

• Add 40 tasks to a namespace called Public Tasks Test (WIP). Assign all tasks to user "public" at creation.
• Allow public users access to the task page, workspace page, and inspect task page.
• Allow public users access to open & pending tasks which are assigned to user "public". Hide these tasks from authorized users.
• Allow public users access to closed tasks assigned to themselves.
• When task is submitted, use the task ID instead of get_next_task()
• Reassign public tasks to submitting username on close. (Still need to think through security implications of this)
• Add a new tab called Shortcuts to the dashboard page and add the ability to view all tasks assigned to user "public" through this new tab. This is helpful because no google account corresponds to the "public" assignee. We can add other shortcuts in the future if we want.
• Add contact email to task page for unauthorized user
• Fix a bug associated with choosing NO to tracking operation IDs when creating a namespace
• Fix a spellcheck bug for the bot

[dxenes1]

• create task bucket for public and pull from that instead of hard-coded assignee.
• if a user is not authorized, pull from public and immediately re-assign to their own username. when they close the task, close with their username.
• (OPTIONAL) add expiration date to tasks to ensure tasks that remain uncompleted return back to queue

[dxenes1]

Closing to merge with #419