Added user location button in the Calculate screen

The user location button should fire up itself when the Calculate screen is mounted as we have userLocationButton={true} but it does not. This is the open issue for react-native-maps on github https://github.com/react-community/react-native-maps/issues/2010. However on forcing a state change it shows up the button and I have implemented the same in the code.
Link to apk https://drive.google.com/open?id=1bEywGptprWossrCX7Vch_IcCDDZf5IoX