scratch-audio depends on sound property being called md5 even though it refers to md5+file ext,
so this property cannot be renamed just yet.

This reverts commit dee7195f.

Swapping out default project with sb3 version. This will be refined as the sb3 spec gets fleshed out.

* 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

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