Showing/hiding 'more options' in the different types of variable prompts based on var type provided from scratch blocks

I created the project in the wrong place.

Remove the WebGL checks from the error boundary. Instead, just do not
render the stage if it is not supported.

Additionally render the canvas at a multiplier of the device pixel
ratio, so we get hidpi images for supported screens. The fixed CSS
sizing allows us to do that.

The problem was that on Edge, flexbox apparently can grow canvas
elements, whereas on Chrome/FF the canvas width/height is respected. No
problem, we can set the width/height in CSS to fix it, which
conveniently allows us to also fix the low-res-on-retina-screens problem
at the same time.

* Added object.assign polyfill

* Fix IE load failure

Don’t call `(window.AudioContext || window.webkitAudioContext)()` if platform is IE

Catch any other errors, and display Browser unsupported in error-boundary.

If for some reason there are no other errors (unlikely), preview-modal will still check for IE and show the unsupported modal.

Polyfilling Object.assign is enough to get through load and show the modal for IE. We can always switch to `babel-polyfill` if there are others needed later, but for now this is smaller.

temporary patch for #1205.

Add Error Boundary (has componentDidCatch method) to handle WebGL errors and display an informative message. 

* Update libraries re: feedback. Resolves GH-1182 GH-1187 GH-1188 GH-1189 GH-1184

* Rename astronaut in space theme

- reduced the load time of the preview modal assets
- changed cursor to ‘pointer’ for modal buttons