UI to remove stream members

[gnprice]

On the info page for a stream, we have an option to add subscribers, but not an option to remove them. It would be good to have a UI to remove people from a stream.

This would probably happen as an additional feature on showing a list of the people in the stream, #3656 .

See feature request in chat.

[wilsonfurtado2000]

i think we should give this access to the admin rather than everyone