Set VC's title independent from possible tab bar button label

[dingbat]

Makes setTitle set the view controller title through navigationItem to prevent interference with a possible tab bar label.

Fixes https://github.com/wix/react-native-navigation/issues/113.

Using .navigationItem.title overrides the title property of a view controller (which is automatically set by the tab bar controller to be the tab button title) when displaying it in the nav bar. See "The Middle Item" here: https://developer.apple.com/library/ios/documentation/UIKit/Reference/UINavigationController_Class

As far as I can tell, no other actions that change the title (push/reset/etc) should need this, as they either don't apply to a tab bar controller's root element, or they replace it with a new VC entirely.

[drorbiran]

Hi, we wanted to update you that we are currently postponing the processing of pull requests.
Please refer to React native controllers evolution, we'll appreciate your feedback.