Add fullscreen button to ComponentPlayground

[kitten]

Fix #316
Depends on #391

Adds a fullscreen button to the ComponentPlayground that uses the Fullscreen API.

[carloskelly13]

Looks great 🎉

[kitten]

Quick note after testing Safari w/ @carlospaelinck: this doesn’t take into account yet that spectacle might already be in full screen mode

Edit: It turns out that I can't replace the fullscreen element for Safari by closing and reopening as browsers only accept a fullscreen request as part of a user interaction.

[ebertmi]

@philpl I implemented a custom "editor" component and also integrated a fullscreen mode by putting the content into a wrapper with absolute positioning and a z-index. This works even if spectacle is already in fullscreen mode.

[kitten]

@evertmi the way to go if we need more fullscreen-able components is definitely an abstraction, maybe even a portal component, to support Safari.

For now this should definitely be sufficient for the current use case