Add a "duplicate" feature for plugins

[rjb0026]

I've found that I will often need many of the same plugin that are all configured the same with the exception of one or two properties. It would be nice to have the ability to set up one plugin as "template" for the common properties, duplicate it a bunch of times, and then fix up the non common properties. Something like the "duplicate" feature like the one added in RVIZ.

Right now I'm thinking about adding "duplicate" as an option in the drop down context menu that appears when you right click a plugin and adding the 'Ctrl+d' hotkey. I'm not opposed to adding a "duplicate" button next to the "add" and "remove" buttons either if others think that is useful.