Error when deleted user name is clicked in Active Members list on dashboard

[kojiagile]

For instance, in Active Members list of All Platforms activity in dashboard, a user kojistudent has been deleted from the CLA toolkit, but it is listed in it. When the name is clicked, an error page is shown.
Not sure users are likely to be deleted in usual operation...
Anyway, either deleted users should not be listed in the list or back-end process should check the existence of users so an error won't occur.

[tommarmstrong]

It looks like a lot of the models refer to users using their username instead of allowing the Django ORM to take care of relations. I think that all code where the username is being used should be refactored to use the ORM as it would automatically take care of this and make for much more maintainable code

[tommarmstrong]

Same cause as #31

[kirstykitto]

Yes - agreed Tomasso. Good idea.