Don't make everything public.
Don't poll for SFML events.

Since Qt now handles displaying the window, we don't have to poll
SFML for any "window closed" events anymore. Instead, the rendering
window can be closed once the application shuts down.
Don't check key presses if window isn't focused.
Simplify setting key map.
Use initializer lists for memory arrays.
Merge pull request #19 from Ventero/fixes

Various fixes