Merge ThreeThree Sprint 20

Requesting merge for:

MOSYNC-2968 PanoramView crash when shown without children
MOSYNC-2847 Add property for Screen that return whether is shown or not.
MOSYNC-2481 Initial screen orientation always portrait
MOSYNC-2949 Handle orientation events on WP: send orientation value, and new events: EVENT_TYPE_ORIENTATION_DID_CHANGE and EVENT_TYPE_ORIENTATION_WILL_CHANGE
MOSYNC-2842 Create new syscall that performs a camera snapshot and returns the image data via custom event.
MOSYNC-2751 iOS runtime modularization