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/HowYouCanHelp/tests/__snapshots__/howYouCanHelp.test.tsx.snap

@@ -8,29 +8,35 @@ exports[`rendering of the HowYouCanHelp checks if various text fields are visibl
     </h2>
     <ul>
       <li>
-        View our 
+        View the 
         <a
           href="/en/methodology"
         >
           Methodology & data
         </a>
-         page and send us feedback.
+         page and send feedback.
       </li>
       <li>
         Find communities of interest and 
         <a
-          href="mailto:Screeningtool-Support@omb.eop.gov"
-          target="blank"
+          class="usa-link usa-link--external"
+          data-cy=""
+          href="mailto=Screeningtool-Support@omb.eop.gov"
+          rel="noreferrer"
+          target="_blank"
         >
-          share your feedback
+          share feedback
         </a>
         .
       </li>
       <li>
         Respond to our request for information on 
         <a
+          class="usa-link usa-link--external"
+          data-cy=""
           href="https://www.federalregister.gov/"
-          target="blank"
+          rel="noreferrer"
+          target="_blank"
         >
           federalregister.gov
         </a>