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/AdhocMetricEditPopoverTitle_spec.jsx

@@ -36,7 +36,7 @@ describe('AdhocMetricEditPopoverTitle', () => {
   it('renders an OverlayTrigger wrapper with the title', () => {
     const { wrapper } = setup();
     expect(wrapper.find(OverlayTrigger)).to.have.lengthOf(1);
-    expect(wrapper.find(OverlayTrigger).dive().text()).to.equal('My Metric\xa0');
+    expect(wrapper.find(OverlayTrigger).find('span').text()).to.equal('My Metric\xa0');
   });
 
   it('transfers to edit mode when clicked', () => {