Add drop downs for login/out and user name displaying

[Mirv]

Solve scrolling bar via css / jquery drop down rather than

- if user_signed_in? && !current_user.anonymous?
  %li.sidebar-nav-item
    // TODO - assess value of showing user name
    // #{logged_in_email(current_user)}
    // \-
    = link_to 'Log Out', destroy_user_session_path, method: :delete
- else
  %li.sidebar-nav-item
    %a.js-scroll-trigger{:href => new_user_session_path} Log In
    // TODO - implement drop down for sign up on mouse over?
    // \-
    // %a.js-scroll-trigger{:href => new_user_registration_path} Sign up

[Mirv]

Removed comments to keep code clean as git also documents this for us.