Refactor nav controls

• make generic control instead of re-using specific one
• make it more responsive friendly
• cleanup some mess
• removed btn-green css class

Usage example:

# With tabs
.top-area
  .nav-links
    %li
      %a My Projects
  .nav-controls
    input
    .dropdown
    .btn

# With text

.top-area
  .nav-text
    Awesome text
  .nav-controls
    input
    .dropdown
    .btn

cc @rspeicher

Refactoring for !2677 (merged)