successfully sets user_id into session upon login
    * /logout clears session hash
    * adds helpers folder
add login/logout helper methods
    * potentially wrap helper methods in a module
set current_user to nil upon logout
show/hide DOM based on @current_user
    * info on ruby's double pipe equals: http://www.rubyinside.com/what-rubys-double-pipe-or-equals-really-does-5488.html