AccelerometerModel: kept working on hold detection
AccelerometerModel: added tracking for hold times.  The model watches the accelerometer to see if the device is in a “hold” state, here just meaning it’s sitting on its back, not moving, and it determines what proportion of a preset time interval the wait has completed (i.e. 50%, or 100%).  This data is packed in the acceleration data notification for use by the bubble view, ultimately.
FirstViewController: added a couple lines to pass the ratio of delay completed into the bubble view.
LevelBubbleView: added support for a circular “loading bar” that follows the normal, gray outer circle around as it approaches 100%.  To facilitate this, added a loadingRatio property.  This view no longer supports non-square shapes.  It will not draw correctly if this is attempted.