Request to join project

[jwalsh]

From @jwalsh on May 27, 2015 1:20

When viewing a project a user should be able to request to join a project.

When viewing a project a list of project collaborators should be shown.

As a project owner I should be able to add people who requested to join a project.

Copied from original issue: HumanDynamics/MassScaleSocialSystems#51