Made another mass of accessibility improvements

- Set proper semantic tags for main parts of content.
- Removed focus-trap from tag manager/autosuggest.
- Set better accessibility labelling on tag manager.
- Updated collapsible sections to be keyboard navigatable.
- Improved input focus styling to better fit theme.
- Updated custom styled file picker to be accessible via keyboard.

Related to #1320

resources/assets/js/vues/components/autosuggest.js

@@ -6,6 +6,7 @@ const template = `
             @input="inputUpdate($event.target.value)" @focus="inputUpdate($event.target.value)"
             @blur="inputBlur"
             @keydown="inputKeydown"
+            :aria-label="placeholder"
         />
         <ul class="suggestion-box" v-if="showSuggestions">
             <li v-for="(suggestion, i) in suggestions"
@@ -66,23 +67,23 @@ const methods = {
     },
 
     inputKeydown(event) {
-        if (event.keyCode === 13) event.preventDefault();
+        if (event.key === 'Enter') event.preventDefault();
         if (!this.showSuggestions) return;
 
         // Down arrow
-        if (event.keyCode === 40) {
+        if (event.key === 'ArrowDown') {
             this.active = (this.active === this.suggestions.length - 1) ? 0 : this.active+1;
         }
         // Up Arrow
-        else if (event.keyCode === 38) {
+        else if (event.key === 'ArrowUp') {
             this.active = (this.active === 0) ? this.suggestions.length - 1 : this.active-1;
         }
-        // Enter or tab keys
-        else if ((event.keyCode === 13 || event.keyCode === 9) && !event.shiftKey) {
+        // Enter key
+        else if ((event.key === 'Enter') && !event.shiftKey) {
             this.selectSuggestion(this.suggestions[this.active]);
         }
         // Escape key
-        else if (event.keyCode === 27) {
+        else if (event.key === 'Escape') {
             this.showSuggestions = false;
         }
     },