create 'remove user from project' endpoint

[chrismclarke]

should remove a single user from a project, given the project name and user name.

[chrismclarke]

I'm pretty sure this can be done by sending a Delete request in the same format as to #10. This needs to be tested.

[chrismclarke]

whoops, wires crossed, that's to remove a form from a project.

To remove a user from a project it's the same as adding a user to a project, but including
{
remove:true
}
in the user object

so uses same format at #8