Split client and server tests into separate Jest "projects"

- server tests now use the "node" jest environment, removing the
  mongoose warning
- both projects can use their own jest.setup.js file

Author: andrewn

client/jest.setup.js

@@ -0,0 +1,8 @@
+
+// eslint-disable-next-line import/no-extraneous-dependencies
+import { configure } from 'enzyme';
+// eslint-disable-next-line import/no-extraneous-dependencies
+import Adapter from 'enzyme-adapter-react-16';
+import '@babel/polyfill';
+
+configure({ adapter: new Adapter() });