Harmonise parameter input praxis into Problems

[TorkelE]

Currently, this is the way to create an ODEProblem using MTK:

using ModelingToolkit

@parameters t σ ρ β
@variables x(t) y(t) z(t)
@derivatives D'~t
eqs = [D(x) ~ σ*(y-x),
       D(y) ~ x*(ρ-z)-y,
       D(z) ~ x*y - β*z]
de = ODESystem(eqs,t,[x,y,z],[σ,ρ,β])

ODEProblem(de,[x => 1., y => .2, z => 3.],(0.,10.),[σ => 1.,ρ => 1.,β => 1.])

while this is an incorrect notation

ODEProblem(de,[1., .2, 3.],(0.,10.),[1.,1.,1.])

When creating ReactionSystems using the new DiffEqBio rework one does not declare the variables and parameters, hence I enabled the notation

ODEProblem(rs,[1., .2, 3.],(0.,10.),[1.,1.,1.])

where rs is a ReactionSystem. This is the only type of system where this is possible.

We will need to decide on an input praxis, and ensure that it is similar across all system types.

Reference: #425

[isaacsas]

Best issue title I've seen this year!

[ChrisRackauckas]

Fixed by lowering via conversions.