Refactor primary navigation JS to use Drupal Behaviors

At first glance this is a refactor of beauty! I have a couple nitpicks below since we're refactoring the whole thing. I know that most of these are leftovers from the previous code.

Note that I'm still going to do some additional cross browser and device testing. But I don't see anything that looks like it would cause issues.

Thanks!

1. +++ b/js/navigation.js
   @@ -6,85 +6,97 @@
   +      if (e.keyCode === 27) {
   

   Some cleanup. We can use e.key === "Escape" here.

2. +++ b/js/navigation.js
   @@ -6,85 +6,97 @@
   +      if (e.key === 'Tab' || e.keyCode === 9) {
   

   Once again, we only need e.key

3. +++ b/js/navigation.js
   @@ -6,85 +6,97 @@
   +      var mobileNavWrapper = context.querySelector('#' + mobileNavWrapperId + ':not(.js-' + mobileNavWrapperId + ')');
   

   These variable names seem a bit off to me. The header-nav element wraps all of the navigation (mobile and wide). Maybe just call it "navWrapper"?

4. +++ b/js/navigation.js
   @@ -6,85 +6,97 @@
   +        mobileNavWrapper.classList.add('js-' + mobileNavWrapperId);
   

   We shouldn't use the js- to indicate that this is processed, the js- prefix is used for selectors that JavaScript will be using. Maybe something like "processed-". Not sure if Drupal has a convention for this type of stuff.

Tested both regular and mobile navigation across Chrome, FF, Safari, and IE11. Works great!

Looking good!

+++ b/js/navigation.es6.js
@@ -1,100 +1,135 @@
+      if (e.key === 'Tab' || e.key === 9) {

I'm fixing this on commit!

Committed! Thanks!

Re-closing since yarn:build has been run, committed, etc.