User Story 65, EXTENSION: Admin disables a user account

[iandouglas]

As an admin user
When I visit the user index page
I see a "disable" button next to any users who are not yet disabled
I see an "enable" button next to any users whose accounts are disabled.
If I click on a "disable" button for an enabled user
I am returned to the admin's user index page
And I see a flash message that the user's account is now disabled
And I see that the user's account is now disabled
This user cannot log in
This user's city/state and orders should not be part of any statistics.

DO THESE STORIES FIRST:

• User Story 55, Admin User Index Page

Checklist:

• base tests are written
• base code is written to pass tests
• edge case ("sad path") tests written (if required)
• edge case code written (if required)
• code is reviewed
• branch is merged
• all tests still pass

child of #52

child of #125

depends on #58