fixes and an extention to the header/footer marcos

- fix #34896: header/footer macros $F and $f show bogus information for linked parts, a non-existing path resp. filename.
Let's use rootScore()'s name instead.

- fix #34421: header/footer macros $M and $m don't work in linked parts (show empty).
Let's use rootScore()'s tdate and time instead.
Also once a score has been modified, hence marked dirty, these marcos don't reflect that.
Let's use current date and time in this case.

Remaining issue: having changed score/part and saved it, these macros still don't reflect the change, the file needs to get closed and reopened. Here some method to refresh this fileInfo() data would be
needed.
 
- add a $N macro to footer/header to show page number on page one only if there is more than one page in the score/part