Rebuild navigation

[danielemery]

Since introducing the activity feed the navigation bar is too crowded on mobile to add any further links.

It's also been requested that a button to explicity return to the quiz list is included in the navigation bar (rather than needing to know that the quizlord title will take you there).

In order to faciliate more links the following ideas are considered:

• Replacing the link text with an icon on mobile
• Implementing a "hamburger" menu when mobile is detected

An additional feature that should be considered as part of this rework should be highlighting which page you are currently on.