Issue 408: ARMA and ARIMA models

[seabbs]

This draft PR closes #408 and starts towards adding submodels everywhere. To close this out I need to:

• Remove all standard deviation priors from latent models
• Use HierarchicalNormal as the default residual process
• Decide if we need helper constructors for our current models (i.e do we want AR(std_prior)) to work)
• Write arma and arima helper functions. Deciding how much flexibility to expose (plan is to restrict to just p,q,r priors and the standard deviation prior of the residuals).
• Review and improve tests

[github-actions]

Try this Pull Request!

Open Julia and type:

import Pkg
Pkg.activate(temp=true)
Pkg.add(url="https://github.com/CDCgov/Rt-without-renewal", rev="issue408", subdir="EpiAware")
using EpiAware

[SamuelBrand1]

Hey do you need any help with this one?

[seabbs]

no its okay I just need to get off primarycensoreddist and then can get this unstuck

[SamuelBrand1]

Seeing updates 👍

[seabbs]

ha yes this PR has got really out of hand - just doing some lsthm admin stuff then back on this