Upgrades to the availability process with new assignment type

[JonathanGarro]

Right now, the availability reporting is handled by assignments. That means a user has to already have an assignment in order to provide their availability. However, in practice, we'd want to have folks that haven't actually supported yet to be able to report as well. I see a relatively simple solution here that could have additional benefits to workflows:

• Add a button to the emergency page that appears if the user is not already listed as a remote supporter with a label like "I want to support!". Clicking this will create a new assignment with a different status (I'd propose "On Standby"). That means they would have a provisional assignment that doesn't get counted on any rolled up stats, but are able to submit availability.
• All users listed as being on standby are put into a table only visible to admins and SIMS Co's.
• If a given user then ends up providing support, a single button on that table would convert their status to "Active".

[JonathanGarro]

Decided to go with a simpler implementation of this idea.