Merge pull request #49 from Chabrier/master

gvle: refactoring the Dynamics Editor Dialog
vle: switching to 2013

Upgrade all date in source code comment (c, h, cpp, hpp),
{vle|gvle|vfl}.rc.in and glade file to 2013. (closes #50).
gvle: add a duplicate value function

A duplicate item has been added to the contextual menu of the values
list of the condition editor dialog window.