Grigori Adventurer counter tweaks

[joseasoler]

The current implementation gives too much weight to the palace. Huge bonuses like the one from the palace should go down to 10, and the other costs should be scaled around it. It should also be tweaked in a way that the first and second adventurers are achieved in roughly the same turns than with the vanilla implementation.

Relevant posts :

http://forums.civfanatics.com/showpost.php?p=12147110&postcount=5 http://forums.civfanatics.com/showpost.php?p=12149308&postcount=7