Bugfix and balance walls / siege

[elexis]

Walls are one of the greatest remaining imbalances in alpha 19 due to multiple bugs and imbalances:

Before the attack:

• Walls can be built very fast r17312
• The number of wall turrets is not limited by area ("min-distance"),

During the attack:

• Walls are instantanously repaired and without any resource costs #3707
• Pathfinder of the attacker yielding unexpected paths in mazes of obstructions
• Wall turrets having more range than every other unit
• Attackers fail at dealing enough damage
  • Regular champs are not (and shouldn't be) useful in attacking walls
  • Elephants die too quickly
  • Ranged siege doesn't deal enough damage and is destroyed by wall-turrets

After the attack:

• Walls don't decay in disconnected territory #3340

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#3707 and #3340 should be fixed individually. The other issues (besides pathfinding) can be addressed in this ticket. Not everything must be fixed for a20, but it should become more reasonable.

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See also from: ​https://wildfiregames.com/forum/index.php?/topic/20621-good-players-usually-say-no-walls-in-the-multiplayer-lobby/&do=findComment&comment=314820

[elexis]

Two alpha 19 replays of games that took extremely long due to the pattern described above.

[fatherbushido]

(wrong comment)

[fatherbushido]

There is inheritance from template_structure_defense

    <Hack>15.0</Hack>
    <Pierce>25.0</Pierce>
    <Crush>3.0</Crush>

So with r17312, walls have 33% more crush armour compared as a19 balancing, HP is a bit decreased but for many civs, HP is hardcoded in their own templates (gauls, brits, romans iirc).