Adding new assignees using invite code

Since the authentication flow recently changed to logging using an OTP-token instead of a magic-link, the invites sent out to task-assignees should be respectively updated. This pull requests proposes various changes for enabling this feature.

To make this work, new assignees will be sent an email with a link that has their email-address prefilled. On this page they are asked to provide the OTP-token from the email. Note that this is technically equivalent to the general login flow, and since they have been invited, they can also go to the general login-page and login as usual. Any time a user - new or existing - is assigned to a task, their metadata is updated to include the new task_id. When they (re-)log-in, they will see a flash message on the home page indicating that they're assigned to a new task and can start annotating with the provided link.

The logic for inviting users has been implemented for the task import page, the manual creation of assignments page and the updating of task assignments page.

MaastrichtU-BISS / lawnotation

Adding new assignees using invite code #27