Summary:
The actual badgeColor prop causes the following error when run on device with a version inferior to iOS 10 like iPad 2 and iPad mini 1.
`*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[UITabBarItem setBadgeColor:]: unrecognized selector sent to instance 0x7968be80'`
This PR fixes it by checking at runtime if the selector is available for the current running version.
It also makes the color available at start by using the variable `self.barItem`. Currently, the color appears only after a reload.
Closes https://github.com/facebook/react-native/pull/12354
Differential Revision: D4598036
Pulled By: shergin
fbshipit-source-id: 9f104fc27db51213a54273e33c5a22f1b350c55e
ca2741609a