Consider making more things classes

[martingkelly]

It may be a natural fit and simplify our function prototypes.

[martingkelly]

More specifically, we could add the following classes:

• Project. This would reduce the number of arguments we have to pass into each builder.
• Manifest. This would make it more natural to access config properties, as opposed to passing loose strings everywhere.
• Workspace. This would avoid having to pass around root, ws, etc. into every function.

We already have Command classes.