Should help with smaller screen sizes, where the ratio is different (like some chromebooks)

Initial SB2 Import UI (button in preview modal + import modal that can load projects via url). Preliminary validation on url, still needs error handling.

Images are draggable by default, but when used within buttons or as
clickable elements, they should not be draggable because starting a drag
accidentally prevents the click event.

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

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

* 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.

- 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.

Changed existing string ids to use the convention `<repo>.<component>.<identifier>`

Alphabetize all the things

  Commit fceba4e8 introduced new sizing behavior for the stage in
  order to fit everything in a 1024 width. Adopted this same behavior
  for the StageHeader component.

To show the "Add Extension" button, you must now add `?extensions` to
the URL used to load the GUI.

  1. Fixed issue with sprites not being dragable when stage zoomed.

  2. Fixed issue with coordinates of mouse position being wrong when
     stage is zoomed. This was caused by the renderer not being
     resized when zooming/unzooming.

  3. Refactored zoom control to separate react component/containter
     with global reducer for isZoomed, which is passed to the stage
     container. This allows for the zoom control to zoom the stage
     menu and stage as seperate containers.

  4. Added icons zoom/unzoom for stage zoom control. Moved icon
     position to be part of stage menu floating to right of start/stop
     buttons.

Add class name props to the components, and fix positioning for the green flag to be reusable.

It wasn't ever necessary. Still allow configuring this path in the GUI in case of different paths to static files for scratch-blocks.

With jscodeshift thank God

Attaching the storage module in `vmListenerHOC` means it can propagate
down to the GUI, stage, and blocks naturally. The default VM property
value has been removed from those places so that we're not instantiating
extra VM instances any more. Instead, using one of those components
outside of the `vmListenerHOC` framework will require providing a VM
instance as a property.

* Covers parts of these issues: GUI layout panes (#69), sprite libraries (#12), import buttons (#64), menu bar (#67), and sprite info area (#53)

~ Refactored layout pane structure by removing `display: flex` from `.box`, by default. Declaring flex instead only where specifically needed. This helped fix layout quirks, and should help us avoid hard to find issues related to nested flex boxes

~ Added descriptive classnames to boxes/containers/wrappers. Moved more padding, margins + layout into these wrappers to help with component reusability.

~ Set up a spacer unit variable inside `gui.css`, to start keeping consistent padding, margins and rounded corners between panes. Used [CSS/PostCSS Modules](https://github.com/css-modules/postcss-modules-values) to avoid SCSS dependency.

~ Refactored inline styles from JSX, into CSS files. 2 reasons: a) prepping for reuse of CSS Module variables. b) Feels easier to debug complex flex layouts when all the styles are in one place vs JS/HTML/CSS syntax mixed together

~ Added menu bar into layout via new component, and sprite info header in sprite selector pane, with stubs for the labels + forms. Sprite items are correctly scrolling, while leaving the header fixed, in Chrome. Mostly working in FFx. Not working in Safari, IE yet.

~ Style pass on library modal

~ Experimenting with a few different transition styles: Logo in menu bar, sprite library items, Add buttons.