Restore maximized state of window

On Linux and Windows there is a maximized state that isn't the
same as simply restoring the window's size on Mac OS X.
Store maximized state in window dimensions
Remove unused method
Add maximized parameter
Document darwin check
Maximize window after it is shown
Don't maximize on Mac OS X

Just setting size, position, and full screen state is sufficient since
there is no explicit maximized state.
Merge pull request #3276 from atom/ks-restore-maximized-state

Restore maximized state of window