Adding 'devise' gem.
Adding flash messages to main layout.
Initial 'devise' configs.
Devise: adding User model (default configs - to be changed).
Devise: updated user model & devise configs: don't want recovery and registration - users will be created only manually.
add-admin rake task: moved code into User model (for now). Added 'environment' task dependency to make things actually work.
Added 'sign-in', 'sign-out' links.
User: adding authentication to controllers!