Resolves https://github.com/LLK/scratch-gui/issues/1713

Add a jest unit test for making sure the number is rendered out when
provided and not when not provided.

Fix integration tests for the recent chrome stable update

* 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

- implements welcome to the preview modal, and unsupported browser modal.
- will need assets updated in Jan.

* Implement GH-830: Add coming soon tooltips

This implements coming soon tooltips for:
* the small stage size
* save, load and language

It also creates the component that can be copied over into the paint editor for use there as well.

Lastly, this does a small refactor on the full screen implementation to include multiple small screen sizes too.

Localizes the pen extension:
- loads all pen locale information - may want to consider dynamically loading locales later.