Add external link icons & all outstanding changes from Living copy (#1173)

* Refactor Footer component

- Make Footer component align to normal folder structure
- Make links in Footer use LinkTypeWrapper, which will allow icon to be added to all external links in one place

* Add Trussworks link to LinkTypeWrapper

* Add icon to SurveyButton comp

* Add launch icon to About page cards

* Add launch icon to FederalRegister link

* Refactor Methodology page

- Add Source and Available for fields to dataset Cards
- refactor data structure for dataset Cards to handle more than 1 source
- update constants file
- modify SASS for source list items
- update snapshots

* Add copy changes; How you can help and territories

* Update methodology section with copy changes

* Swap out all email links with <LinkTypeWrapper>

- update tests

client/src/components/DatasetCard/tests/__snapshots__/datasetCard.test.tsx.snap

@@ -15,29 +15,38 @@ exports[`rendering of indicator dataset card checks if component renders 1`] = `
       
     </div>
     <ul>
+      <li>
+        <span>
+          Used in: 
+        </span>
+        All methodologies except for training and workforce development
+      </li>
       <li>
         <span>
           Responsible Party: 
         </span>
+        Census
+      </li>
+      <li>
+        <span>
+          Source: 
+        </span>
         <a
+          class="usa-link usa-link--external"
+          data-cy=""
           href="https://www.census.gov/programs-surveys/acs"
           rel="noreferrer"
           target="_blank"
         >
-          Census's American Community Survey
+          American Community Survey
         </a>
+         from 2015-2019
       </li>
       <li>
         <span>
-          Date range: 
+          Available for: 
         </span>
-        2015-2019
-      </li>
-      <li>
-        <span>
-          Used in: 
-        </span>
-        All methodologies except for training and workforce development
+        All U.S. states and the District of Columbia
       </li>
     </ul>
   </div>