[fix] Support recursive object definitions

[dansanduleac]

Before this PR

We import references to other conjure objects eagerly, i.e. we import the class directly, like so:

from .package.MyType import MyType

but if MyType is an object/union whose fields end up referencing back to MyType, python will never succeed in importing this way, because the imports will form a circular dependency.

After this PR

We place relative imports (that start with .) at the bottom of the file, such that if they cause a recursive import of an attribute from inside the module currently being loaded, it would have been defined already.
This solution has been identified thanks to this recommendation found online.

[ferozco]

Unfortunately the modules already re-expose the types so that from ..product import StringExample is actually importing the class StringExample. You would have to introduce the concept of namespace imports so that you could do something like import ..product.StringExample as foo

[dansanduleac]

Yep, @ferozco - rewrote this as we discussed earlier.

[ferozco]

Closing in favour of #12