docs: Update all documentation for @loopback/rest refactor

[kjdelisle]

Summary

After the refactor to move all of the HTTP/REST items into their own package, we need to update all of the documentation that involves use of those modules and functions.

Acceptance Criteria

Review and update the documentation. Make sure the updated code snippets work! (You can use acceptance tests or example apps to help you with verification.)

loopback.io pages:

• Thinking in LoopBack
• Key concepts
• Getting started
• Using Components
• Creating Components
• Calling other APIs
• Testing Your Application
• Migration guide
• Crafting LoopBack 4 - No code snippet in this page
• Reference

loopback-next:

• review and fix per-package READMEs (authentication, etc.) (Diana)

[dhmlau]

@kjdelisle , I can work on reviewing the READMEs since I've started on one already.

[crandmck]

We also need to update the API docs, specifically we need to add the new package to https://github.com/strongloop-internal/apidocs.strongloop.com/blob/master/ts-repos.json

[dhmlau]

@crandmck , I could submit a PR for the change in ts-repos.json if you want. But I'm not sure how to verify it.

#622 is created

[kjdelisle]

Closing as complete!