Update MFE to use the new “brand-openedx” repository. (#283)

* Update MFE to use the new “brand-openedx” repository.

This will allow the MFE to be re-branded by overriding this default implementation.  More detail here:

https://github.com/edx/brand-openedx

* Removing unused frontend-component-header module.

This app doesn’t use frontend-component-header.  That it was a dependency is confusing and led me to believe I needed to wait for its rebrand to continue - not so.  Removing the unused dependency.

* Adding quick comment describing the structure of gated_content

* Fixing course exit styling

* Changing LinkedIn icon

* fix: fix Instructor toolbar button styling

* Bumping footer, platform, and paragon versions.

* Using configured logo and favicon.

Co-authored-by: Carla Duarte <cduarte@edx.org>

public/index.html

@@ -4,7 +4,7 @@
     <title>Course | <%= process.env.SITE_NAME %></title>
     <meta charset="utf-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
-    <link rel="shortcut icon" href="/favicon.ico" type="image/x-icon" />
+    <link rel="shortcut icon" href="<%=htmlWebpackPlugin.options.FAVICON_URL%>" type="image/x-icon" />
     <% if (htmlWebpackPlugin.options.OPTIMIZELY_PROJECT_ID) { %>
       <script src="https://www.edx.org/optimizelyjs/<%= htmlWebpackPlugin.options.OPTIMIZELY_PROJECT_ID %>.js"></script>
     <% } %>