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/dashboard/SliceCell_spec.jsx

@@ -10,7 +10,7 @@ describe('SliceCell', () => {
   const mockedProps = {
     slice,
     removeSlice: () => {},
-    expandedSlices: () => {},
+    expandedSlices: {},
   };
   it('is valid', () => {
     expect(