Smithy 1.7 upgrade (#340)

* Upgrade to Smithy 1.7

Two changes:
1. Add support for shape renaming. Since renaming doesn't apply to operations, errors, or resources, this was actually a fairly narrow change. I intentionally
maintained the ability to generate a model without a service shape, I expect at some point, some one will just want to make some Rust structs.
2. Add support for map-driven query params.

* Update APIGW model

* Fix bugs in httpParams implementation

* Cleanup logic and add one more test