[MU4] Straight flags now spaced better

[asattely]

Traditional flags on notes are reduced outside the staff such as to make sure the hook ends up at a certain vertical point, but this is meaningless for straight flags. The shortening that straight-flagged notes do now follows the same rules as beams:

[RomanPudashkin]

@asattely please rebase it

[RomanPudashkin]

@asattely sorry, but please rebase it again...

[asattely]

Rebased