Integrating the compiler algorithms from uflacs into ffc for fast compilation of complicated forms for FFC

It's a bit difficult to come up with a detailed plan for this up front because I will have to refine the interface while we're implementing. Below follows some coarse steps to follow. 1) Implement this blueprint: https://blueprints.launchpad.net/ffc/+spec/gradient-representation-for-scalability I expect this alone ...