Reorganize host and component code

Now that we're storing code for components and hosts in the repository, we should likely reorganize the code tree of the repository itself.

Some issues:

- We have a python host that should probably be close to the rust host (`example-host` assumes Rust, but we should probably have folders for different langauges)
- Components should be more consistently organized under a scheme like `/`, rather than what we have now (i.e. `python/adder`, `js/adder`, `rust/calculator`, etc)