Chart for gain value evolution

I would have liked to see the evolution of my gain value over the time. So I have added a new "Evolution" menu item  (to be compared to the repartition chart displayed in the "Summary" menu item) in the right click menu of the sell portfolio panel.
I have created a new JDialog chart to display this information : 
* gain value evolution
* loss value evolution
* cumulative gain value evolution
* cumulative loss value evolution

The new strings that I have added are not translated yet.

If you think this modification can be useful for others, feel free to merge this pull request.