Add Al Kharid free-to-play content - #208

Port the Al Kharid content module from the getpitchfork/silo fork,
completing the town's free-to-play surface:

- Toll gate: Open / Pay-toll(10gp) on both gate leaves, with free
  passage after Prince Ali Rescue.
- Prince Ali Rescue quest on the quest engine (varp.princequest).
- Market shops: Zeke, Dommik, Gem Trader, Ranael, Louie Legs, the
  two general-store clerks (inv.generalshop1), plus Karim's 1gp
  Talk-to-only kebab sale and the Silk Trader haggle greeting.
- Ali Morrisane greeting on the Al Kharid man populace slot.

Raw-cache overlays ride along: content.banker tagging for the two
bank-booth bankers, anchored border guards, OSRS-accurate shop
sell/buy/change percentages for the named shopkeepers, and the
palace double-door closed/open content-group pairing.

Integration tests for all of the above live in the fork
(getpitchfork/silo); the GameTestState harness they run on has not
been upstreamed.