Applet on Mac uses Cmd-click for right mouse, should be Ctrl-click

Unix convention is that Ctrl-click is treated as right mouse button e.g. opens context menu if present.
This is now consistent in Jalview Desktop (JAL-2077) but not in the applet.
Desktop (correct):
- checks event.isPopupTrigger()
Applet (incorrect):
- checks SwingUtilities.isRightMouseButton(event)
   - this is true for Cmd (Meta)-click, but false for Ctrl-click
Result: applet behaves differently to the desktop.
For example, in the ScalePanel:
Desktop:
- Cmd-click to select additional columns, Ctrl-click to open context menu (hide/reveal)
Applet:
- Cmd-click and Ctrl-click behaviours are reversed