Update vert_bars.js

Code now supports adding new data elements (one or more at a time), in addition to continuing to support existing data element updates and associated transitions.  New elements are created off screen, then transitioned into the visible area.  Bars are updated first, then the text (this may be changed later).  Update function now calls a separate "drawUpdate" function that eliminates the need for the update function to be called twice before any changes are reflected in the SVG elements.