Add support for nested colocated components.

[rwjblue]

This is a more targetted implementation that aims to avoid the breaking change nature of #414 (and #398 before it).

Closes #414

[rwjblue]

Currently failing due to the issue reported in socketio/engine.io#589. Will attempt to pin engine.io to the prior release.

[rwjblue]

Tested in the octane blueprint as well:

❯ ember g component foo --component-structure=nested
installing component
  create app/components/foo/index.hbs
  skip app/components/foo/index.js
  tip to add a class, run `ember generate component-class foo`
installing component-test
  create tests/integration/components/foo-test.js

~/sandbox/octane-app-20190923 master*
❯ ember test
Could not start watchman
Visit https://ember-cli.com/user-guide/#watchman for more info.
Environment: test
cleaning up...
Built project successfully. Stored in "/var/folders/mt/yt2qjpl93ls98lrkrs81rzch000pzv/T/tests-dist-2019823-38750-2drncw.6nefj".
ok 1 Chrome 77.0 - [401 ms] - Integration | Component | foo: it renders
ok 2 Chrome 77.0 - [1 ms] - ember-qunit: Ember.onerror validation: Ember.onerror is functioning properly

1..2
# tests 2
# pass  2
# skip  0
# fail  0

# ok