Create better default values for threshold/history

[fnoop]

No description provided.

[kripper]

I guess the threshold and history was needed in order to avoid bouncing between markers.
In https://github.com/kripper/vision-landing-2/ we don't land on a marker center, but on a landing point that is defined relatively to all markers.
So there is no bouncing and any marker can be used.
Actually we prefer to use the biggest detected marker because "more pixels" => "better estimation".

In case the marker detection wouldn't be robust enough, appriltags also provides a confidence value that could be used.