accessToken filelds should be annotated with @NonNull in all mapbox-java services

[osana]

All subclasses of com.mapbox.core.MapboxService need a required accessToken to be specified when a Service request is done.

accessToken should be always annotated with a @NonNull annotation.

At the moment there is an inconsistency in the project and the following classes have @Nullable annotation

MapboxDirections
MapboxGeocoding
MapboxMatching
MapboxOptimization
MapboxStaticMap

Only MapboxMatrix, MapboxSpeech and RouteOptions (which is not a Service subclass) have it annotated correctly with @NonNull