Temporary "fix" to conflict between JBrowse track pinning and WebApollo selection/dragging.  Allows testing of pinning and selection/dragging, but if tracks are scrolled "under" pinned tracks they actually show up above it. Actual solution will probably involve redoing how ghost drag coords are calculated, and what div they are attached to.
Changed WebApollo plugin to reflect change to block strategy in JBrowse, blocks are no longer divs but instead have a div property, block.domNode.
Another fix needed for SequenceTrack to adjust to new block strategy where block is not itself a div but instead has a div property, block.domNode