warn about duplicate names

warn about duplicate names. If ticked this will warn you if you use a note name that matches an existing note; the match case-sensitive. Tinderbox will allow duplicate note names but you should be wary as any such name duplication can have unwanted side effects when it comes to HTML or text export. This is because any code that uses note names as a parameter may not be able to correctly resolve the correct target note from which to extract data.