Fix duplicate check in note editor

Duplicate checking was broken. The content of the Note was never being updated to reflect the content in the text boxes in the editor, so the dupe check was only ever running on old values. I made it update the relevant (first) field before a dupe check (but then put the old value back since there is a modification check later on).

I also removed the confirmation dialog on dupes. There have been a few complains about it, and it just adds an extra step to modifying notes when the highlighting should already be enough to signal a duplicate.