Addition of custom JSON viewer (#51)

* Added accessible JSON viewer.

This change introduces a new JSON viewer component. This component is
based on the FAST-React `<TreeView>` component with minor modifications
(which take place within CSS definitions). It removes the
react-json-view component, which cannot be navigated at all with the
keyboard.

* Cleaned up frontend package dependencies

* Removed out-of-date refs to react-json-view

* Fixed CR comments, added key= property to TreeViewItems

* Code review feedback / consolidation

* Removed unsafe-eval from CORS policy

package.json

@@ -22,5 +22,6 @@
     "start": "node ./scripts/run-frontend",
     "run-tests:shared": "node ./scripts/run-package-task -- --package-name network-console-shared --task-name test",
     "ps": "node ./scripts/generate-pseudoloc"
-  }
+  },
+  "dependencies": {}
 }