Access to ios configuration methods

It would be cool if the react native SDK could bridge access to those methods:
```objc
[TheoremReach getInstance].navigationBarTextColor = @"#FFFFFF";
[TheoremReach getInstance].navigationBarText = @"iOS Demo App";
[TheoremReach getInstance].navigationBarColor = @"#17b4b3";
```

This would let us configure without writing native code.

thanks