PvP Arena, economy & client improvements

• Added free-for-all PvP at Prontera (166, 198), with no EXP or item loss.
• Sitting now restores empty HP/SP to full in 120 seconds. NPC sell prices are 75%, with withheld zeny entering the Treasury.
• Poison Spore and Red Mushroom drop Karvodailnirol at 1%.
• Other Settings groups Cast Cancelling, SP Reserve and Normal Attacks; set skill level to 0 to remove it.
• AzzyAI is on by default for new installs. The cash shop is currently empty, and the login screen has been refreshed.