Upgrade to React==16.4.1 & Enzyme==3.3.0 (#5359)

* Bumping react==16.4.1 &  enzyme==3.3.0

The upgrade was pretty smooth except for a cryptic message coming
out of react-select around running multiple copies of React. It turns
out the `common` bundle had React and was conflicting with explore and
dashboard apps, only in 16.x. This somehow wasn't a problem in 15.x
outside of the wasted resources.

Running 16.4 should bring in all sorts of perf improvements and features
we've all been waiting for.

https://reactjs.org/blog/2017/09/26/react-v16.0.html

TODO: react-bootstrap-datetimepicker isn't compatible with React 16

* Trying to deprecate react-bootstrap-datetime

* Moving forward

* Reintroducing tests

superset/assets/spec/javascripts/explore/components/DisplayQueryButton_spec.jsx

@@ -2,7 +2,6 @@ import React from 'react';
 import { expect } from 'chai';
 import { describe, it } from 'mocha';
 import { mount } from 'enzyme';
-import { Modal } from 'react-bootstrap';
 import ModalTrigger from './../../../../src/components/ModalTrigger';
 
 import DisplayQueryButton from '../../../../src/explore/components/DisplayQueryButton';
@@ -27,6 +26,5 @@ describe('DisplayQueryButton', () => {
   it('renders a dropdown', () => {
     const wrapper = mount(<DisplayQueryButton {...defaultProps} />);
     expect(wrapper.find(ModalTrigger)).to.have.lengthOf(2);
-    expect(wrapper.find(Modal)).to.have.lengthOf(2);
   });
 });