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.

Also extract the "supportedBrowser" logic into a helper (rule of 3)

* Player mode

Add isPlayerOnly property on GUI. Move isFullScreen into mode reducer with isPlayerOnly.

Full screen needs to be a separate prop so that GUI knows what to show when exiting full-screen (either player-only or full editor).

- set `gui-body * {box-sizing: border-box;}` instead of expecting it to be set by the enclosing component/playground, and removed uses of content-box (adjusting sizes as needed) 
- Added `!isPlayerOnly` to the conditions for draggable sprites
- rewrote player example to use player mode.

The initial intl store expected an object with an `intl` key, not the intl object as returned by `injectIntl`.

Also changed GUI proptypes to accept Object as well as String for projectData to avoid warnings.

Allow intl to be passed in to GUI as a prop (rather than having to be already in the store)

Add Error Boundary (has componentDidCatch method) to handle WebGL errors and display an informative message.