feat(templates): support nested templates to create nested routes

[philnash]

Fixes #122

This adds a directory property to TemplateFileInfo and then uses that to place the files in the correct nested directories.

Contributing to Twilio

All third-party contributors acknowledge that any contributions they provide will be made under the same open-source license that the open-source project is provided under.

• I acknowledge that all my contributions will be made under the project's license.

[philnash]

The Pika CI check seems to need a package-lock.json or npm-shrinkwrap.json. But as a package, we shouldn't be checking that in (and it was removed in PR #118). Can we remove the Pika CI check @dkundel?

[dkundel]

Yeah I'll remove it. Not sure why it requires it :( maybe for performance reasons. I'll review the PR in a few