cache parameters, namespacemap and reorder_parameters

[KristofferC]

For a big model I see the following change in ODEProblem construction time:

# before
 27.275824 seconds (323.85 M allocations: 11.322 GiB, 8.87% gc time)

# after
 21.425995 seconds (270.93 M allocations: 9.439 GiB, 9.54% gc time)