User accounts

[timsk]

Registering as a volunteer will create a user account.

We will need to import data relating to existing registered volunteers, albeit after perhaps some GDPR-related pruning of inactive people.

Users will need to be logged in to claim a shift.

Procedure for logging in should be as quick and simple as possible, particularly on mobile but also on bigger screens.

Logging in when you have an upcoming delivery shift will highlight that you have access to your route (within a customisable time window).

There will be several "admin flags" that can be set for particular users that gives them access to more functionality, e.g. removing people from rotas, accessing volunteers' contact info, auto-texting volunteers to fill rotas, accessing clients' contact info, cancelling orders (one-off, until a given date, or permanently), sending an email/SMS to all clients (or a subset thereof), etc.