Nested subitems

#### What's this PR do?
Ties into the paginated consumer branch, but allows us to have access parent and children items from an initial fetch. This is beneficial in we save on queries (for instance, in needing to present the parent's item card alongside the subitem).

#### Where should the reviewer start?
query-config has a change to include children.
item.js now instantiates a parent attribute with a fully formed item.
#### How should this be manually tested?
```js
z = backlog.get(5645)
z.get('parent').get('title')  // this returns the parent's title
```
#### Any background context you want to provide?
Part of the reports view work. This allows us to query for the transitive dependencies for easier showing in the UI.

Needs the paginated consumer code merged first.

#### What are the relevant tickets?
Refs #8190
#### Screenshots (if appropriate)
#### What gif best describes this PR or how it makes you feel?
![](http://mlkshk.com/r/114YN)
#### Definition of Done:
- [ ] Is there appropriate test coverage? (e.g. ChefSpec, Mocha/Chai, Python, etc.)
- [ ] Does this PR require a Selenium test? (e.g. Browser-specific bugs or complicated UI bugs)
- [ ] Does this PR require a regression test? All fixes require a regression test.
- [ ] Does this PR require a blog post? If so, ensure marketing has signed off on content.
- [ ] Does the [knowledge base](https://sprint.ly/docs) need to be updated?
- [ ] Does this add new dependencies? If so, does Chef, M4, or PIP requirements need to be updated?
- [ ] Will this feature require a new piece of infrastructure be implemented?
- [ ] Are any new services fully automated in Chef?
- [ ] Are there ChefSpec tests for the new Chef recipes/cookbooks?
- [ ] Does this PR require new Mixpanel or GA events?
- [ ] Is there appropriate logging included?