Fix some scaling difficulties occuring upon wheel scrolling
Use the _placeScrollBar method in _updateScrollBar for improved scale change handling
Add new unit tests covering scaling edge cases for ScrollBar.js
Refactor ScrollBarSpec
Refactor ScrollBar._updateScrollBar to not use _placeScrollBar
Remove ScrollBar event handlers on mousedown to prevent extra handler binding bug
Add comments around event handler binding/unbinding, and merge stopUpdatingScrollbar and removeDocumentEventWatching methods
Fix drag event bug that prevented handler unbinding
Merge pull request #35 from WebFilings/BOOKS-3560

HY-811: Fix ScrollBar Scaling Bug