Refactoring of Actor Integration

[bowd]

"- Single different MarketPriceGenerator models into separate classes to unload MarketPriceGenerator\n- Structure TraderStrategy and strategy classes; extract common methods into TraderStrategy\n- sell_gold and trading_regime have overlapping functionality => unite\n- get rid of self.sell_amount and self.order and introduce self.metaorder\n- Create a metaorder strategy for the trader to sell to the market\n- Fix failing convex optimisation for arbitrage trader strategy"