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`.

With locally loaded png image

This reverts commit c177706a.

The VM refreshWorkspace will eventually lead back to onWorkspaceUpdate,
which will call refreshSelection itself.

This reverts commit 5b9e8aa0, reversing
changes made to 4cb65dc5.

Also, simplify the paint editor wrapper by passing in most props from redux. Since the paint editor will only receive relevant props, remove shouldComponentUpdate. Clean up PropTypes as well.