[Frontier] The bounded area is defined in meters (double)

While here, remove undesired markup (used for folding).
[Frontier] Fix the validity of the seed value.

A seed outside of the bounded area is still valid.
And the weight map and the raster have their own way to manage
value outside the image. (throw exceptions)

While here, remove some too verbose output and try to respect the 80-char length
of the code.
[frontier] Fix "jump" in frontiers computation.

Appeared when scale is not equal to one.
[frontier] Use internal parameters to simplify function calls.
[frontier] Add a maximal size for the frontiers.

Avoid too big frontiers (split them).
(typically : one big circle around the robot).

May "minimize" the impact of some issues with the lookout choice.
(And delegate the decision to higher levels, like xares decision making
function, which is a good thing).