Request to join existing project

[ewingrj]

We should get more validation on this before building, but I was thinking it would be useful to be able to request the join an existing project.

We could send the admin an email/notification and they can accept or deny the request.

Currently when a new user creates an account, the are redirected to the "Create A Project" page. It would be nice if they we maybe displayed 3 options:

1. View Existing Data (query page)
2. Join Existing Project
3. Create a new Project

This idea came from looking at the Ira Moana contribution docs where they ask people to create a GeOMe account, then say do not create a project but instead email them so they can add you to the Ira Moana project