Implement React Context API

- Move API GET request to /v2/config out to the top level of our App.
- Store /v2/config response data in sessionStorage.
- Use Context API to pass down relevant data to Organizations component.
- Wrap our AnsibleSelect component as a context consumer and pass in the list of Ansible Environments of the logged in user.
- Clear sessionStorage object when user logs out.
- Update unit tests.

__tests__/pages/Organizations/views/Organization.add.test.jsx

@@ -1,8 +1,29 @@
 import React from 'react';
 import { mount } from 'enzyme';
-import OrganizationAdd from '../../../../src/pages/Organizations/views/Organization.add';
 import { MemoryRouter } from 'react-router-dom';
 
+let OrganizationAdd;
+const getAppWithConfigContext = (context = {
+  custom_virtualenvs: ['foo', 'bar']
+}) => {
+
+  // Mock the ConfigContext module being used in our OrganizationAdd component
+  jest.doMock('../../../../src/context', () => {
+    return {
+      ConfigContext: {
+        Consumer: (props) => props.children(context)
+      }
+    }
+  });
+
+  // Return the updated OrganizationAdd module with mocked context
+  return require('../../../../src/pages/Organizations/views/Organization.add').default;
+};
+
+beforeEach(() => {
+  OrganizationAdd = getAppWithConfigContext();
+})
+
 describe('<OrganizationAdd />', () => {
   test('initially renders succesfully', () => {
     mount(