Move guiMiddleware to `reducers/gui.js`, and use it in `app-state-hoc`

scratch-gui exports `index.js` instead of just GUI container.

Since compatibility-testing got switched to use the player mode, it doesn’t need any of the stage/controls components.

* Export initial states for each reducer
* combine all gui reducers (excludes scratchPaint and intl)
* combine all initial states to create default guiState for preloading in www
* expect all of the gui state to be accessible at `state.scratchGui`

GUI will export a reducer to be included in the enclosing component’s redux when GUI is used as a library. The app-state-hoc is moved into the playground examples to provide a store when GUI is being used stand-alone.

Specifically in 2.0:
- Monitors cannot be dragged in fullscreen/player
- List monitors cannot be resized, have items added using the button or have their values edited.
- Slider monitors still work.

Only call updateProject to load the project if there is a project id, or it’s the default project id.

- better split of hash-parser/project-loader unit tests.