Updates iOS One Signal SDK to 2.12.6. This is a major update since it:
- Removes deprecated UIWebView usage from original SDK (OneSignal/OneSignal-iOS-SDK#522)
- Fixes a problem while building it with Xcode 11 (williamrijksen#85)
- Removes deprecated API call to IdsAvailable
- Adds CoreGraphics and WebKit must haves frameworks
- Updates to Titanium 8.x SDK
- Uses TitaniumKit framework and sets CLANG_ENABLE_MODULES to true on project configuration