Allow bot to trade only with money earned from trade/giving by admins.

[peti446]

Changes the buying process to take into account the gold that the bot currently owns. This allows admins to stop bot abuse to generate enormous sums of gold by selling items. There is already a measure in place by limiting the bids per X time, but this takes it a step further by not generating any more gold (unless the admins add funds to the account) while also removing some form the economy (cuts).