added download function for geofence and rallypoints

[mattes-bru]

No description provided.

[julianoes]

See suggestions. The naming must be consistent, otherwise the auto-generation won't work. Best to test it before making the PR.

However, you probably can re-use the actual mission items in the requests, e.g.:

message DownloadGeofenceRequest {}
message DownloadGeofenceResponse {
    MissionRawResult mission_raw_result = 1;
    repeated MissionItem geofence_items = 2; // The geofence items
}

[mattes-bru]

Sorry, I was too fast on the PR button. I updated naming & comments