Add ScrollBar Component

**NOTES**
This is a new PR against master instead of ScrollBarExample.

**ULTIMATE PROBLEM**
A standard, reusable scrollbar component was needed for use with ScrollLists.

**SOLUTION**
A new UI component was added in wf-uicomponents, called ScrollBar. It's based off of Robbie Lamb's example.

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Please review: @tonyhelvey-wf @ericdebusschere-wf @robbielamb-wf @timmccall-wf 
FYI: @shanesizer-wf