Turned off displaying labels for sequence alteration annotations.
Another fix for block --> block.domNode changes in JBrowse
Fixed problem with floating arrows to keep within view, in DraggableHTMLFeatures.  Problem was that still had partially working method updateFeatureArrowPositions() in DraggableHTMLFeatures, which was overriding new call in HTMLFeatures to new working method HTMLFeatures.updateFeatureArrowPositions.
Fixed zoom level settings to ensure that max zoom scale is scale at which sequence residues are rendered in SequenceTrack.