Add Lego WeDo 2.0 extension to library

Add compatibility testing example page

Scroll to extension category only when loading from library

Load extension library data from a js file

Fix project json loading through storage

Allow loading the default project while offline

/ht @paulkaplan

Previously we tested the ProjectLoader helper object, but now all loading is confined to storage. Unfortunately I wasn't able to get enzyme to wait for the storage promise to resolve within componentDidUpdate, so I can't test the actual results of storage.load, just what it was called with.

eslint-plugin-import doesn't like these inline loaders.

I tried unsuccessfully to configure the recommended solution with `eslint-import-resolver-webpack`, but we should come back to this.

With this change we only use `xhr` in the `CostumeCanvas` component.

This way the instance can be reused, which allows access to non-deprecated `DataFormat` and `AssetType`.

Update scratch-storage to the latest version 

Wait for scroll animations correctly 

Prevent loading duplicate extensions

Bring back the 'contains' operator block

Update enzyme-adapter-react-16 to the latest version 

Add block chunking to toolbox xml

With locally loaded png image

Instead of using svg-url-loader only

Update toolbox before ScratchBlocks inject and Give  IDs to some shadow blocks