Made a mass of accessibility improvements

- Changed default focus styles
- Updated dropdowns with keyboard navigation
- Updated modals with esc exiting
- Added accessibility attirbutes where needed
- Made many more elements focusable
- Updated hover effects of many items to also apply when focused within

Related to #1320 and #1198

resources/assets/js/components/chapter-toggle.js

@@ -11,12 +11,14 @@ class ChapterToggle {
     open() {
         const list = this.elem.parentNode.querySelector('.inset-list');
         this.elem.classList.add('open');
+        this.elem.setAttribute('aria-expanded', 'true');
         slideDown(list, 240);
     }
 
     close() {
         const list = this.elem.parentNode.querySelector('.inset-list');
         this.elem.classList.remove('open');
+        this.elem.setAttribute('aria-expanded', 'false');
         slideUp(list, 240);
     }