[v14 ready] Latexify improvement

[TorkelE]

Makes some improvements to make Latexify automatically use our new expand_registered_functions function to expand mm and similar. Now this is done by default for reaction, ode, and sde forms. Also, setting the kwarg expand_functions=false disables this.

using Catalyst, Latexify
rn = @reaction_network begin
    (mm(x,v,K),d), 0 <--> X
end
latexify(rn, form=:ode, expand_functions=false)

[isaacsas]

One comment, otherwise LGTM.