[CB-7158] fix geolocation for ios 8

See https://issues.apache.org/jira/browse/CB-7158.

The change will use the new [APIs introduced by iOS 8](https://developer.apple.com/library/prerelease/ios/documentation/CoreLocation/Reference/CLLocationManager_Class/index.html#//apple_ref/occ/instm/CLLocationManager/) to ask user permissions before using the Geolocation function. 

Can some one please review this and merge it back to master? I have already signed & filed the Apache CLA.