setFocus and x and y shake magnitude

cameras can now set their focus to a point if they do not have an actor
to follow; added separate shake magnitudes for the x and y direction
Merge remote-tracking branch 'origin/master' into dev-josh
Camera Zoom issue #55

Cameras can now zoom in/out to a specified scale, with an optionally
specified duration of time over which to zoom to that scale. This closes
issue #55
Merge pull request #187 from eonarheim/dev-josh

Dev josh