Flag introduced restricting altitude limits to tracking

Some mounts (like the Avalons) have the tendency to pass altitudes below 0 even if the target is 0 or greater. This leads to the situation that altitude limits for such mounts are too restrictive.

For such situations, a new flag "Tracking only" is introduced for the altitude limits. If the flag is set (which is not the default), the altitude limits are only used if the mount is in a tracking state. While slewing or parking, the limits are ignored.