Added iOS 8 support for location service requests

Hi there,

according to Apples documentation of CLLocationManager (https://developer.apple.com/library/prerelease/ios/documentation/CoreLocation/Reference/CLLocationManager_Class/index.html#//apple_ref/occ/instm/CLLocationManager/) it is required to call either `requestWhenInUseAuthorization` or `requestAlwaysAuthorization` on a CLLocationManager before you start updating the location under iOS 8.
It is also necessary to define - depending on the chosen authorization type - either `NSLocationWhenInUseUsageDescription` or `NSLocationAlwaysUsageDescription` in the projects `Info.plist`.

I have added an enum `ClusterLocationAuthorizationType` as well as a new method to request the permissions for a specific authorization type. Backwards compatiblity is maintained by letting the former method definition choose `ClusterLocationAuthorizationTypeAlways` by default.

Cheers,
Tom