[470306][470427] Adds generic Plot Editor and removes context menu item duplication

Created by: SmithRWORNL

This adds a generic, service oriented plot editor, which can automatically open any file for for which a visualization service exists which advertises its ability to create a model for that file type. Users are prompted as to which visualization service to use in case of conflicts, and the UI allows for the plot to be changed from one type to another.

Also, a bug in which items in certain IPlot implementations' context menus would be displayed multiple times if the context menu was reopened has been addressed.

Bug: 470306 https://bugs.eclipse.org/bugs/show_bug.cgi?id=470306 Bug: 470427 https://bugs.eclipse.org/bugs/show_bug.cgi?id=470427 Signed-off-by: Robert Smith SmithRW@ornl.gov