For Travis CI - another attempt to fix iOS 64-bit packaging.
[ci package]

- When performing CI build for iOS platform, suppress all warnings. Non-CI build will still receive them.
- Automatically instruct Travis CI to do packaging when AngelScript or LuaScript API have changed.

Additionally, enhance iOS-specific Urho3D_universal custom target to perform initial check to see a rebuild is really necessary.
For Travis CI - switch CI build to use OS X build environment.