config plugins

[PatrickAlphaC]

It would be nice to be able to do like:

mox install aave-addresses

or like:

mox plugin add aave

Or something, where it downloads from either pypi or github (or both? Maybe it would be easiest to keep it the same as the install setup?) where you can install contract addresses without having to go to the docs.

Rationale

This would make it easier to do scripts on common addresses/tokens.

Risks

There is a risk here, if the addresses change, we'd have to stay on top of it. That could be pretty spooky. Maybe we label "well known" addresses that are unlikely to change with something different from addresses that are likely to change.

More thoughts

It might be a good idea to "lazy load" named contracts. As in, we don't load a named contract unless explicitly called on by manifest_named. This way, we could have a massive number of named contracts without having to load every single one.