Make wall tiles destructible

[nugarin]

All wall tiles should be destructible - they could have an insane amount of hitpoints and regenerate when not fully destroyed.

[chris]

I thought about this as well, but than "real" walls somehow lose their advantage to constructed walls. What would be nice, if one could transform plain terrain to swamp and vice versa. This way one could create some kind of moats in front of your defensive structures.