GUI: Improve Context Menus

[jGleitz]

As discussed in #607, our GUI should offer context menu entries at more places to allow the user to start the analysis from where he is working

• I think there should be a context menu entry for all SEFF elements we measure, not only resource demanding internal actions.
• I know that most folks at the SDQ look at repositories by simply opening the .repository file. It would be good to have the context menu entry there, too:
  
  • This enable users to select components more easily (because selecting in a list is easier than in a diagram
  • This would also enable users to make a mixed selection like “Measure these three components and half of the SEFF of this component, but leave out this RDIA becaues that it a lot of time”