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>

package.json

@@ -34,11 +34,11 @@
     "url": "https://github.com/edx/frontend-app-learning/issues"
   },
   "dependencies": {
-    "@edx/frontend-component-footer": "10.0.11",
-    "@edx/frontend-component-header": "2.0.6",
+    "@edx/brand": "npm:@edx/brand-openedx@1.1.0",
+    "@edx/frontend-component-footer": "^10.1.0",
     "@edx/frontend-enterprise": "4.2.3",
-    "@edx/frontend-platform": "1.5.4",
-    "@edx/paragon": "12.0.5",
+    "@edx/frontend-platform": "1.8.0",
+    "@edx/paragon": "^12.3.1",
     "@fortawesome/fontawesome-svg-core": "1.2.32",
     "@fortawesome/free-brands-svg-icons": "5.13.1",
     "@fortawesome/free-regular-svg-icons": "5.13.1",
@@ -59,10 +59,10 @@
     "redux": "4.0.5",
     "regenerator-runtime": "0.13.7",
     "reselect": "4.0.0",
-    "truncate-html": "^1.0.3"
+    "truncate-html": "1.0.3"
   },
   "devDependencies": {
-    "@edx/frontend-build": "5.4.0",
+    "@edx/frontend-build": "5.5.1",
     "@testing-library/dom": "7.16.3",
     "@testing-library/jest-dom": "5.10.1",
     "@testing-library/react": "10.3.0",
@@ -73,7 +73,7 @@
     "glob": "7.1.6",
     "husky": "3.1.0",
     "jest": "24.9.0",
-    "jest-chain": "^1.1.5",
+    "jest-chain": "1.1.5",
     "reactifex": "1.1.1",
     "rosie": "2.0.1"
   }