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

* Change default variable name to 'my variable'. 

* Update integration test to look for 'my variable'. Re GH-1162

* Resolve issue with space in integration test

Update opcode label for monitors.

* Implement paint-75: Add blank costume button

* add backdrop icon, use default name

thanks @fsih !

Replace the placeholder illustration.

* Add coming soon extensions to the library

This implements #1074

* don’t call `onSelect` when disabled

thanks @paulkaplan!

* add speech image to coming soon extension

* add feedback form

This implements #829

* small style updates to the stage buttons

from @carljbowman

* remove `stageSize` for now

We eventually need this, but not yet, and it’s causing lint failure.