Allow declaring methods and publications under models

[ebroder]

@zarvox - I know you've expressed concern in the past about how TypedMethod and TypedPublication were leading to a very flat code structure, so I decided to see if I could come up with a better alternative. I'm not entirely sure if I think this is an improvement, but I think it does have some nice properties.

Almost all of our publications and models are associated (or at least primarily associated) with a model. This is reflected in the way we name our methods ("verbNoun"). However, we previously placed all methods in a single flat directory and did the same with publications.

Instead, allow declaring methods and publications as part of creating a new model class. This has the convenient side-effect of reducing the imports you need to operate on a model to just the model class itself. It also makes the internal identifier for a method or publication match how we refer to it in code (e.g. ChatMessages.methods.send).

For now, the implementations of the methods and publications are still in the same files as before; that's potentially something to reevaluate in the future. Additionally, it arguably makes it harder to enumerate all methods and publications, but that might be an acceptable tradeoff.

[ebroder]

Oh another note: we can probably find a model to house all of our methods/publications under, but it's not always going to be clean. E.g. teamName and mediasoup:debug are both kind of messy. We can either leave those as flat-declarations or jam them under a model (e.g. Settings or try and do a better job of materializing the TeamName model for the former; the latter is...tricky).

Methods tend to be a little cleaner, but e.g. some of the setup page methods are tricky.