Bugfix in setting user.last_login
Close #43. List groups by period on users#roles

Fix login bug in development.
Allow period admins to use the "View a User" function.
Add Airbrake notification when a new user is created
Refactor tabs out of controllers (again)
Add home#list for all users
Refactor admin tools out of users#roles into home#index
Show active roles, not just assignments, in home#list
Confirm addition, deletion of Admin privileges
Set all assignments to 'lost' before updating a period

This should ensure that no ghost assignments exist after account merges.
Fix #32. Add ability to merge User accounts.

Added user.real_id to link to the real_user (the account into which this
user is being merged).
Renamed and restructured functions in ApplicationController. Now have:
* current_user
* original_user
* sudo_user
And now use these helper_functions instead of accessing the global
variable directly.