Upper limit on number of points in geofence #93
Description
Most flight controllers have an upper limit on the number of points they can handle in the geofence. We don't know the limit in advance and it would be a waste of resources to query it for every drone in the swarm, but we should allow the user to specify an explicit upper limit in the preferences somewhere and show a large warning box if the current geofence has more points. (Otherwise Skybrush would happily attempt to upload the geofence to the drone, then fail while doing so and give no indication to the user about what went wrong).