Jalview-JS/JAL-3253-applet JAL-3266 Varna fix.

Jalview-JS/JAL-3253-applet JAL-3266 Varna fix.

For some reason, the JPopupMenu was being added to the JPanel with
Component.add(), and then removed with Component.removeAll()
-- during the painting process. This caused it to appear on the
window as its unstyled <ul><li>... list.

Also, during painting, Component.setBackground() was being set.
This is very nonstandard and cannot be recommended.
I am surprised it works in Java.

Working now in JavaScript. Export to SVG and PNG are very nice!