Support OAuth 1.0

[blakeembrey]

We need to support OAuth 1.0 clients in the JavaScript generator. That means a promise-based reusable OAuth 1.0 library like https://github.com/mulesoft/js-client-oauth2. There also needs to be associated documentation generated in the JavaScript client README.

• Create OAuth 1.0 client library
• Integrate OAuth 1.0 with RAML settings and generated client
• Support OAuth 1.0 access tokens (users)
• Add dynamically generated documentation to README

Migrated from mulesoft-labs/raml-client-generator#5.