api.js refactor using classes (#250)

Refactor api.js into an api module where endpoint specific models can be imported and used in components.

__tests__/api/users.test.jsx

@@ -0,0 +1,35 @@
+import Users from '../../src/api/models/Users';
+
+describe('UsersAPI', () => {
+  const userId = 1;
+  const roleId = 7;
+  const createPromise = () => Promise.resolve();
+  const mockHttp = ({ post: jest.fn(createPromise) });
+
+  const UsersAPI = new Users(mockHttp);
+
+  afterEach(() => {
+    jest.clearAllMocks();
+  });
+
+  test('associate role calls post with expected params', async (done) => {
+    await UsersAPI.associateRole(userId, roleId);
+
+    expect(mockHttp.post).toHaveBeenCalledTimes(1);
+    expect(mockHttp.post.mock.calls[0]).toContainEqual(`/api/v2/users/${userId}/roles/`, { id: roleId });
+
+    done();
+  });
+
+  test('read users calls post with expected params', async (done) => {
+    await UsersAPI.disassociateRole(userId, roleId);
+
+    expect(mockHttp.post).toHaveBeenCalledTimes(1);
+    expect(mockHttp.post.mock.calls[0]).toContainEqual(`/api/v2/users/${userId}/roles/`, {
+      id: roleId,
+      disassociate: true
+    });
+
+    done();
+  });
+});