add use_profile_values to preferences

This merge request adds user_profile_values to preferences . But to my surprise this merge request is not needed after doing all the work I noticed that there's "Edit Header" menu item , which opens a dialog to edit header and this dialog pretty neatly handling the header of po file . It even has a checkbox "use my options to complete following entries" same as this merge request .I earlier failed to notice that key "use_profile_values" is getting used there . So this merge request can be closed as it is just adding redundant behaviour .