Random Map: Add Option for port space placement

[Nasenbaer]

It would be nice to add an option to the random map generator, to add port buildspaces.

The following is just brainstorming:

* The generator should make sure, that every island bigger than XYZ has at least one port build space
* The number of port buildspaces should be proportional to the size of the island (or to sqrt(size) or similar)
* If an island has more than one port build space, the build spaces should be evenly distributed.
* Islands with starting positions should have at least one port build space
* The starting position of a player should not block the port buildspace (neither on, nor in the near surounding of the port build sace)

[SirVer (sirver)]

Setting to incomplete for bug sweeping.

[Launchpad Janitor (janitor)]

[Expired for widelands because there has been no activity for 60 days.]

[GunChleoc (gunchleoc)]

Migrated to https://github.com/widelands/widelands/issues/1957