FEATURE: Nav isn't responsive on mobile or smaller windows

[jerdog]

At breakpoint 999px the nav adjusts but never goes to a responsive hamburger menu as is relatively standard, even when on mobile.

There are two issues here as I see it:

1. Neither CSS or ./layouts/partials/navigation.html make allowances for this.
2. Implementing this is a bit messy the way the header.html and navigation.html are separated.

I propose adjusting the site to have a responsive header/nav, and simplify the partials together. I can work on doing this if you want to assign it to me @CoralineAda