Change split=false to split=true in sDCM code.

[david-hofmann]

Update sDCM code to run with the new MTK parameter type. Also, understand which version is more desirable: treat symbolic arrays as such or as single symbolic variables. This is related to:

Neuroblox.jl/src/Neurographs.jl

Line 75 in 28c9d6b

return compose(System(connection_eqs, t, [], vcat(params(bc), p); name, discrete_events = cbs), blox_syss)

and

Neuroblox.jl/src/datafitting/spectralDCM.jl

Line 108 in 28c9d6b

# nr = length(indices[:u])