Bugfix crash on Highlands

Features changes :
Because of the fact that most spawns are initially low yield, the desired yields average in ring 1 and 2 (especially prod) were too often close to minimum values. Some randomness in desired means have been added to have more spawn diversity and the base minimum yields have also been increased to avoid empty spawns outside of the guaranteed tiles.

Adding overall more variations to yields averages in ring 1 and 2 and higher base minimum production.

Floodplains slight avoidance on spawn for non-floodplains civs
Because of the difficulties to balance such spawns that cannot be terraformed and may induce more rng due to disasters, almost all civilizations will prefer to slightly avoid floodplains on ring 1 if possible. Spawns with too many floodplains ring 1+2 leaded to inalterable tiles and could prevents the addition of guaranteed yields. It should not affect to much the civ placement

Removed globally natural settles on 3 prod (gypsum, ivory, deers on hills and fresh water)

Tundra civs :
Guaranteed Deers ring 1 for all tundra civs (hills or forest, can be both)
Higher chances of adding deers during yield adjustments ring around tundra spawn
Snow avoidance : not allowed to spawn with more than 3 snow tiles ring 1+2
Canada will spawn deeper in tundra if possible (less than 3 non tundra in ring 3), while Russia will be closer to non-tundra tiles (at least a few in ring 3)

Bugfixes :
Missing guaranteed 2/2 in ring 1
Missing guaranteed early game strategics
Missing guaranteed Fish+Reef (could be modified if naturally present)
Jungles on grassland (missformed guaranteed aluminium)
Volcano on grassland hills (check volcano before mountain removal)

Spawn balancing :

Guaranteed 3x 4 yields 2/2 tiles in ring 1-2
Guaranteed 1x (at least) 4 yields tile with at least 3 food in ring 2
Guaranteed 2x lux in ring 3 (max 3x lux)
Maximum 2x 5+ yields or 4 yields + extra (faith, culture, science, 3 golds) in ring 2
Guaranteed at least 1 turtle OR 1 reef fish for coastal spawns (and at least 2 workable sea improvements)

Pangaea script update :

=> Pangaea script has been updated to reroll the map if it has too much water in the middle on the map. This should drastically decrease the generation of distorted pangaea (but it is not perfect as you can still have long and thin layers of ocean inside the pangaea, should be possible to make more restrictions depending on feedback)

Map analysis :

=> Each tile is scanned before placing civ, giving a density score for each terrain, feature and resource 6 rings around it => will be used to find better bias

=> A new "peninsula" score is given to every tile, it is calculated with how much land is accessible by walk in 6 steps. A spawn surrounded by too much mountains or water is no longer valid. The score is capped to prevent civs placed first from taking systematically the middle of the map. If a civ can not meet all the minimum condition (usually no bias civ placed last) you may encounter firaxis placement.

=> Forest density has been homogenized overall. Starting from initial 18% on land tiles, have a chance to add a new forest on tiles lacking forest density. Usually ends up to ~25% forest on the map.

Placement :

=> The score calculation to find the optimized possibles spawn placement is based on the "peninsula score" (1), "bias density score" (2), minus a tundra score (3) avoiding getting too close if not desired.
=> Placement order is no longer based purely on tier. It is based on how many tiles are valids for spawn and are respecting the bias of the civ (having a desired resource in ring 2-3 for example). Civ with most restrictions are placed first. No bias civs are still placed last with a increased peninsula score cap.
If a civ has no valid tiles with bias, it uses any valid tiles left (to avoid firaxis placement, for example Spain that has no split available on coast on a pangaea).