Use default toolbox from scratch-blocks

Once another project uses this package, these should become peerDependencies.  Until then install automatically.

While doing so:
- Use ProjectLoader for loading projects
- Stop using loadEmptyProject and supply empty project data
- Move project loading to App, GUI now receives data (as a string - the vm should receive an object eventually)
- Add logging

With only one concurrent build, we can't wait for all the jobs to finish first

Copy-paste-laziness

Update the workspace when changing the target

Because these are peer dependencies, we should be lenient about the required version of React required to use the components.

I didn't use the caret because the x's work and it's obvious what they mean, unlike ^ and ~.

Now they don't have to be built and rebuilt every npm install

Update webpack config and vm usage to match updates in scratch-vm

Also make the toolbox actually get used by scratch-blocks, and update the import of scratch-blocks to use the new shimming method.

Multiple installations of React can cause issues if the package is used just for the components.

This way we can have a consistent style for Node and web code.