KRACOEUS-8308: Adding links in Medusa.  Adding ability to navigate to PD's Notes tab in the Attachments Page.

I don't know if this will work (or is a better solution), but instead of storing the default tab on the form for this you can try using jQuery to simulate a click on the notes tab, after you run the window.open script.  I am not sure if the script will run on the newly opened window or not.  something like this
jQuery("a[id$='@{'PropDev-AttachmentsPage-NotesSection'}_tab']").click()