fixes and an extension to the header/footer macros

- 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.

- 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

- refresh fileInfo() data and update display. This to me seems to be the right thing, independantly of the other fixes, esp. in the light that we no longer have a 'reload score'