FontAwesome v5.0.6 (#1372)

* Update FontAwesome to v5.0.6

* Adapt DiscussionListItem-count icon to match FontAwesome 5 syntax

* Change icon name to match FontAwesome 5.0.6 fas icon

* Add font type prefix parameter to icon helper

* Add Enable Icon Prefix to show icon in Extension Page

* Fix invalid icon behavior

* Change icon name to match FontAwesome 5.0.6 far icon

* Use iconPrefix property on component

* Use full icon class name

* Update icon helper docblock

* Full icon class syntax

js/forum/src/components/TextEditor.js

@@ -70,7 +70,7 @@ export default class TextEditor extends Component {
     items.add('submit',
       Button.component({
         children: this.props.submitLabel,
-        icon: 'check',
+        icon: 'fa fa-check',
         className: 'Button Button--primary',
         itemClassName: 'App-primaryControl',
         onclick: this.onsubmit.bind(this)
@@ -80,7 +80,7 @@ export default class TextEditor extends Component {
     if (this.props.preview) {
       items.add('preview',
         Button.component({
-          icon: 'eye',
+          icon: 'fa fa-eye',
           className: 'Button Button--icon',
           onclick: this.props.preview,
           title: app.translator.trans('core.forum.composer.preview_tooltip')