The collapse in oil prices that began roughly two years ago threw plenty of energy firms and their investors into trouble, but the market plunge has also complicated the financial backing of one of the most prestigious art museums in North Texas. The Kimbell Art Foundation was started in 1936, and the profits from its portfolio of roughly $380 million in assets today supports the Fort Worth museum, which was built in the 1970s. But unlike similar nonprofit foundations, the Kimbell is heavily reliant…