Fix Bad Tests in UIComponents

[JIRA](https://jira.webfilings.com/browse/HY-1053)

KeyNavigatorSpec needed to dispose properly of the scrollLists that it instantiated, and ScrollBarSpec needed to ensure that event handlers got unbound properly by firing `mouseup` events.

**Unit Tests**

No unit tests added. Unit test setup/cleanup has been modified.

**How to +10/QA**

```bash
# skip the following steps if you've already initialized the project
$ git clone git@github.com:WebFilings/wf-uicomponents.git
$ cd wf-uicomponents

# do not skip these!
$ git fetch && 
git checkout HY-1053 && 
./init.sh && 
grunt qa
```

Then, view the browser test runner.

- All tests should pass
- The viewport should not end up blocked
- There should be no console errors

@timmccall-wf 
@lancefisher-wf 
Can we do the append in a `beforeEach` and then remove the element in an `afterEach` to keep from polluting the DOM? Just make it part of the general setup.