Allow adding a realizer/guide by arbitrary name, not requiring they have an account or email

[Powersource]

I think this would be a better option to #78 since I think a lot of the time you don't know the email of the person you wanna assign. Instead of #78 we could maybe have some kind of simple Invite button somewhere else.

[aerugo]

I think that could be a good solution, as long as adding an arbitrary name does not create a person node, as that will quickly clutter the database and make it hard to find people. I also think that it should be clear in the UI that the assigned person is only referenced by name and that they should be encouraged to register and claim the responsibility properly.