Fixes #799 Accept user invitation

[NickSchimek]

We render a Set Password form when the user accepts the invitation from their mailbox. After entering a password they are redirected to the login page.

We could optionally log them in if we choose and display the dashboard.

Fixes #799

Any helpful knowledge/context for the reviewer?

Is a yarn install necessary? no Any special requirements to test? no

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[NickSchimek]

The password setting page could use some styling if we decide to use it

Yeah, we need to add some styling if we're using this Rails view. If someone wants to make the React component for it then that will require some extra work beyond some simple styling. Either way we go I'm fine with. I rather use the simple rails view, rather than booting up the react app to set a password.

Do we want the same thing here, or are we assuming that if they were invited this way that they are already "pre-approved"

Yeah, if a user is invited (which can only be done by an admin) then they are an authorized user at the time of being invited. So no approval is needed.