Books 3560: Desktop Browser: Remove scrubber; add vertical scroll bar.

**NOTES**
There will probably be plenty of changes that this needs before going into wf-uicomponents. Hopefully this is the right PR format for this repo as well.

**ULTIMATE PROBLEM**
A standard, reusuable scrollbar component was needed for use with ScrollLists.

**SOLUTION**
A new UI component was added in wf-ui-components, called ScrollBar. It's based off of Robbie Lamb's example.

**TESTING SUGGESTIONS**
Pull this branch. Then, pull the BOOKS-3560 branches of wf-ui-components and wf-book-viewer. Use bower link to ensure you're using these local versions of the repositories. Then do a books ant and run books normally. View a book in the viewer. You should not see the horizontal slider, and you should see a green scrollbar at the righthand side of the screen.

**AREAS OF REGRESSION**
Viewer scrolling.

**RELATED PRS**
[bigsky](https://github.com/tonyhelvey-wf/bigsky/pull/70)
[wf-book-viewer](https://github.com/WebFilings/wf-book-viewer/pull/20)

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Please review: @tonyhelvey-wf @ericdebusschere-wf @robbielamb-wf @timmccall-wf 
FYI: @shanesizer-wf