[2.2] Arbor and Lys siege issues

[Moose]

Arbor and Lys have issues with AI mesh, as reported by a right proper lad Walscott on Moddb.

I fixed Arbor - added missing mesh (Mostly where archers spawn), corrected existing one and sealed off some areas where AI can get stuck and is not supposed to go there.
Here is the file.
https://www.dropbox.com/s/p8go5b6lp8skhdx/scn_town_21_walls.sco?dl=0

God help the man, who will try to fix Lys - my computer simply couldn't handle that scene.