[TWIG][Templates] Rename inconsistent CSS classes

[CSS] Font size hierarchy refactor
[PLUGINS][MediaFeed] Renamed BeforeFeed event

Type scale hierarchy redone. Bigger line height added, making it easier
to click on links and separate contents.

Feed title added. AddFeedActions replaces BeforeFeed event.
MediaFeed links will now show an icon to the right of the feed title,
smaller footprint and more consistent with the overall design.

components/RightPanel/templates/right_panel/view.html.twig

@@ -1,6 +1,6 @@
 {% block rightpanel %}
     <label class="panel-right-icon" for="panel-right-toggle" aria-hidden="true"
-           tabindex="-1">{{ icon('notes', 'icon icon-right') | raw }}</label>
+           tabindex="-1">{{ icon('chevron-left', 'icon icon-right') | raw }}</label>
     <input type="checkbox" id="panel-right-toggle" aria-hidden="true" tabindex="-1">
 
     <div class="header-panel section-panel-right">
@@ -29,9 +29,9 @@
 
                                 <details class="section-widget-subtitle-details">
                                     <summary class="section-subtitle-summary">
-                                        <h3>
+                                        <strong>
                                             {{ "Additional options" | trans }}
-                                        </h3>
+                                        </strong>
                                         {{ icon('arrow-down', 'icon icon-details-close') | raw }}
                                     </summary>
                                     {{ form_row(blocks['post_form'].language) }}