Make it so the React HTML is loaded from the build

_From @miketamis on November 18, 2018 3:50_

Currently the html for the react is copy and pasted from the react build folder this needs to be fixed so it loads it from the build folder.

I have put a todo by the bit of code with this issue number

```js
// TODO: #9 Make this load from react build
```

_Copied from original issue: miketamis/morph-extension#9_