Add dropdown menu for mobile users

[byBlurr]

Currently, the media query @media (max-width: 640.98px) hides the sidebar and shows a menu icon. When the menu icon shows, this should have functionality. I haven't added the functionality yet as I don't want to just replicate the sidebar. We could maybe have a way to display the same NavMenu, but using text instead of icons for mobile users. This would require tweaking how the menu is displayed depending on a variable or something maybe. I've not thought too hard on it.

Assigned you @Verdillian as you probably have a better idea than me