GUI: Add clarification of what an Internal server error is to user if import fails

git-svn-id: http://simulationcraft.googlecode.com/svn/trunk@18074 3b4652a1-8050-0410-ac47-3d40261b0f8b
GUI: Refactored SC_RecentlyClosedTab to allow for multiple viewers of the same model

git-svn-id: http://simulationcraft.googlecode.com/svn/trunk@18075 3b4652a1-8050-0410-ac47-3d40261b0f8b
GUI: Add recently closed tabs to import tab

git-svn-id: http://simulationcraft.googlecode.com/svn/trunk@18076 3b4652a1-8050-0410-ac47-3d40261b0f8b