API for feeding differential equations into external differential equations solvers

[MasonProtter]

Now that we can generate equations of motion from a Lagrangian (should work in theory for Hamiltonians too but I haven't tried), it'd be really slick if we could pipe that solution into a differential equation solver and get a numerical solution.

@PerezHz works on TaylorIntergration.jl so if he wants to get that running, that'd be great. I'd also like DifferentialEquations.jl support at some point, but just having one integrator available would be a great start.