Danubius random map script with reoccuring gaia ships that take control of the river...

Danubius random map script with reoccuring gaia ships that take control of the river and ungarrison units to attack the players.

Places a fortified gaia village, some gaia units performing a ritual and some towers garrisoned on islands.
The attacker and ship count increases over time.
The attacker composition is randomized per ship and switches from citizen soldiers to champions, heroes and siege engines.
One in three matches takes place at night.

Differential Revision: https://code.wildfiregames.com/D204
Map generation based on patch by Hannibal Barca
Reviewed By: bb, FeXoR
Refs #4354

git-svn-id: https://svn.wildfiregames.com/public/ps/trunk@19434 3db68df2-c116-0410-a063-a993310a9797