* 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`

Prevent crashes resulting from the editing target not being on the target list.

Thanks @paulkaplan

This reduces the complexity of the reducer, as well as how frequently it's run. The VM will emit a targets update after a step if any target info has changed.

These aren't necessary to update in realtime, so throttle them to once every 30ms

Add a new stage selection component that displays the stage separately from the sprite list.

In preparation to split the sprites from the stage, start managing the target list state in a single place.