Update to sync NG UIKit with regualar 1.8.1

• User IDs use different integer formats across platforms, this now unifies them.
• Fix bug #70, will propagate changes to the developer preview branch asap.
• Fix crash on iPad with modal popups.
• RTM Changes - compatible with React Native and others.
  • This update changes messages to be sent as regular messages, rather than RtmRawMessage types.
• Pod and Swift Package now have separate packages, RtmControl can be independent of AgoraUIKit.
• New import statements, use import AgoraUIKit for iOS and macOS.
• Bumped native RTC and RTM SDKs to 3.7.0 and 1.4.10 respectively.
• The RTM package can be included in your project without Agora UIKit.
• Can connect to RTM channel before joining RTC
  Fixes:
• Fix issue where re-joining member's video feed would not render.
• Fix issue where RTM messages are different from Agora UIKit React Native.