Provide a way to use an existing CMMotionManager

[twstokes]

Issue

According to Apple's docs for CMMotionManager, only a single object should exist for the app:

Important

Create only one CMMotionManager object for your app. Multiple instances of this class can affect the rate at which data is received from the accelerometer and gyroscope.

If an app already uses CMMotionManager and imports this library, it could potentially cause side effects with the one in AppLogosScene. Perhaps an existing CMMotionManager could be supplied to this library.

Context

We use gyro data for the Jetpack app landing screen which requires a CMMotionManager object.