Add controls to toggle views.

I've added the javascript to toggle between airport and circular views. There
are still issues with highlighting nucleotides and the like, but this is a
start.
Update rna2d lib
Shrink width so we don't overlap in airport.

In an airport view the plot overlaps with the jmol window slightly. We shrink
the size of the view to prevent this.
Alter airport view plot height.

We need to shrink so the plot height to prevent distortion.
Calculate plot height on the fly.

No need for me to redo the calculation each time, just have the javascript do it
each time we use it.
Hardcode rna3dhub url.

This means we always uses a consistent and the correct format for the data
produced. I don't have the full pipeline working on my machine so the
interaction format may not be the same as on production for all structures. This
avoids this issue.