Implement DeviceMotionEvent API for iOS

[rvdleun]

Goal The user should be able to give permission to let the app get access to the Device Motion Sensors.

Description Due to Apple cutting off access to the devicemotion events on the browser by default, On/Office doesn't work on iOS devices at the moment. With the latest update, a permission API has been added that will give the app access again.

Deliverables

• If the app doesn't have access to the motion sensors on iOS, ask for permission
• Add an explanation to the screen for why the permission is required

[rvdleun]

Implemented with https://github.com/rvdleun/onoffice/pull/25