remember the ticked plot items

[GoogleCodeExporter]

any time i start OHM i have to tick all items I want to see in the plot window.
please remember that selection and restore it on the next start.

(i am not absolutely sure about that behaviour as my PC sometimes crashes due 
to very experimental low-level coding rather than seeing an normal shutdown. 
but that far i can see the ticked items are not remembered under my conditions: 
OHM is forcefully terminated rather than closed the regularl way.)

Original issue reported on code.google.com by [email protected] on 7 May 2015 at 9:27