Add Priority Plus navigation with conditional buttons based on permissions

[robere2]

• Navigation header now dynamically calculates which buttons should be visible versus hidden in a "More" dropdown.
• Buttons can conditionally hidden
  • This is designed for hiding buttons if user doesn't have permission to visit them, however it could be used for any condition.
• Navigation headers buttons are now centered on tablets, where the RPI TV logo is on the left on the screen.
• Add "Account" and "Dashboard" buttons to navbar.