Correct unit spawning for wall towers

[FeXoR]

We will have a functioning wall system soon including wall towers (which allow garrisoning units). The problem is ungarrisoning will spawn units outside the wall, which kinda defeats the purpose of walls.

We probably need some new info in the entity template that allows us to restrict unit spawning angle/position.

[FeXoR]

I think 'structures/celt_wall_gate' has to be rotated by PI, too. It has the gate attached bottom (left in rms) when placed with angle 0. But I think the gate should face outside (like for 'structures/rome_siege_wall_gate'). And all buildings faces with there front (I think that would be outside in case of a wall) top (right in rms) when placed with angle 0.

[historic_bruno]

I believe the model is correct, the entrance will be inside-facing instead of outside-facing. The problem is the unit spawning code doesn't know about walls, that will certainly need to be fixed, so I'm updating this ticket with that info.