overwritting the registration controller for devise, only admin users can create another users.
ensure the user is trying to sign in is active otherwise an error will be rise
FirstName and LastName added to users model
An admin can Add users
An admin can Edit users information like, name, roles, password
An admin can Active/Desactive a user
partial to show form errors
Routes changed to set correct sign_in page as defautl and Dashboard page for authenticated users.

Set route to active a user via patch method
Show users list to be administered by an admin
footer fixed
some menu options added
layout fixed
unnecessary links deleted
firt_name and last_name field added to the new and edit view
active action added to change the status of an user
Merge pull request #5 from lexfernandez/admin_registration

Admin registration