Bay State house sales plunged a stunning 27 percent in July, the biggest drop in 11 years, new figures show, and experts see few signs of a turnaround any time soon. “It’s a pretty dramatic decline,” said Tim Warren of market tracker The Warren Group, which reported yesterday that just 5,070 Massachusetts houses changed hands last month. That’s the market’s worst July sales volume since 1995. “We’re not pressing the panic button yet, but we are watching the trend lines very closely,” Warren said. Prices are also dropping. Warren reported that median house-sale prices fell at a 6.1 percent annualized...