Department permissions for public user accounts

[inghamn]

We want to open up the application to allow non-city employees to be able to add data. Groups like the state Department of Transportation and the University have their own construction crews.

There is interest in creating user accounts for people in other organizations. They should be able to log in, and update closure information for their own departments.

We need to expand Departments into a full-fledged feature of the application, so we have a place to put access control permission.

[inghamn]

After looking at
#57

I'm not sure what we want to do when a user tries to edit an event that they're not permitted to touch. Or when a user does edit one of their department's events, but tries to change the department to something else.

Since #39 is still not dealt with, I don't have any plan on how to deal with these errors.