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/components/AsyncSelect_spec.jsx

@@ -63,7 +63,6 @@ describe('AsyncSelect', () => {
         <AsyncSelect {...mockedProps} autoSelect />,
       );
       const spy = sinon.spy(wrapper.instance(), 'onChange');
-      wrapper.instance().fetchOptions();
       server.respond();
 
       expect(spy.callCount).to.equal(1);