Add ability to collapse and uncollapse a track.

Signed-off-by: Anurag Priyam <anurag08priyam@gmail.com>
Add chevron to indicate collapsible nature of track.

Signed-off-by: Vivek Rai <vivekraiiitkgp@gmail.com>
Increase sidebar z-index to prevent gene overlapping when resizing.

The commmit 9ac2933 introduced the functionality but gene model has a
much higher z-index when resized. This patch takes care of that bug.

Signed-off-by: Vivek Rai <vivekraiiitkgp@gmail.com>