Fix js warnings (#2693)

* react: using prop-types package to fix deprecated React.PropTypes property warning

https://facebook.github.io/react/warnings/dont-call-proptypes.html

* removing babel devDependency because has been deprecated in favor of babel-cli

this fixes a warning during `npm install`:
```
npm WARN deprecated babel@6.23.0:
In 6.x, the babel package has been deprecated in favor of babel-cli.
Check https://opencollective.com/babel to support the Babel maintainers
```

* js: setting ExploreActionButtons.queryEndpoint PropType as required

because it's required in the child component DisplayQueryButton

* js(tests): using object in expandedSlices prop type of SliceCell tests

* js(tests): adding required props to SqlEditor mockedProps

* js(tests): adding required prop editorHeight to TabbedSqlEditors mockedProps

* js: removing unused moments dependency

superset/assets/spec/javascripts/explorev2/components/ExploreActionButtons_spec.jsx

@@ -14,6 +14,7 @@ describe('ExploreActionButtons', () => {
         json_endpoint: '',
       },
     },
+    queryEndpoint: 'localhost',
   };
 
   it('renders', () => {