Use *Properties classes as argument types in Sprout

[martonvago]

[This only affects Sprout, not the checks package.]

Change all argument types for properties arguments from dict to the approperiate *Properties class.
Starting at top-level functions, we should change to using *Properties classes and use them as far down in the function stack as possible.

A natural point for transitioning to dict (so calling compact_dict on the properties) would be when the properties are fed to a check function or the write_json function.

[martonvago]

I had a closer look at the implications of this and I think the check functions should actually be left as is, using dict.
This is because a key use case for check functions is loading a set of properties from the datapackage.json and checking that they meet the spec. These properties are loaded as dict. While it's not difficult to create a Properties object from a correct dict (i.e. a dict that has fields that correspond perfectly to the fields of a Properties class), the whole point is that at this stage we cannot guarantee that this dict is correct -- we have to check it first.

So I think we should still make this change, but leave check functions as is.

[lwjohnst86]

I think this is fine. I don't love the idea of just creating new object types to pass around, but I also come from a functional programming perspective rather than an OOP view.

As long as it is clear and simple, it works for me. I'll have to review the design docs to see how this fits with the change, but 👍 for me for now