Template backend for JuliaDiffEq libraries

The JuliaDiffEq ecosystem provides solvers for all types of problems we solve in TVB with our integrators. Generating code targeting this ecosystem enables (a) testing new solvers than may be worth porting to TVB and (b) verifying our solvers do the right thing.

Expressing regional simulations should be easy, but it would additionally be useful to target their PDE solvers for the surface simulations, to check utility of implicit methods, for instance, which are entirely ignored in TVB for now.