Update pokemon availability, evolutions, and hold items.

[adamnovitch]

• Rework Trade evo levels and learnsets.
• Have Poliwhirl evolve into Politoed with King's Rock same as Slowking
• Have Seadra evolve to Kingdra with Dragon Scale
• Increase presence of king's rock and dragon scale on wild pokemon
  • Have dratini line holding dragon scale? Maybe a rare find on Horsea/Seadra?
  • have kingler hold king's rock maybe? Or any other kingly pokemon.
• Fix other hard to find pokemon like Heracross