Move map-specific biomes to biome files

[elexis]

Some maps hardcode multiple custom biomes and pick one of the variants at random:

• alpine_lakes
• alpine_valley
• gulf_of_bothnia

The data is structured almost exactly like the JSON files already. Having that data in the JSON file means the gamesetup can parse it and the player can select the biome.

Abstracting further, the other maps that don't already use the random bioem system define exactly one biome that they always use (guadalquivir river, volcanic lands).

So every map could have its templatenames, terraintextures and environment settings moved to JSON files.

The random-biome system would become a biome-system that eventually one might think about supporting it in skirmish/scenario maps too. (However biome definitions can include JS, so either these would have to be dropped for skirmish/scenario maps, or we need scripted map generation code on scenario and skirmish maps after loading the PMP file.)