Notation issues - window edges drawing bugs

[bFooz]

Some visual bugs.

1) Grid cut-off area is different than the note cut-off area.

2) Edit cursor have no cutoff area, goes all the way to the beginning. If everything is being hidden, it should be too.

3) Scrolling past the first bar of the item removes bold edge. Should stay bold single-line edge all the time we are within an item.

4) The right edge of the window, wrong drawing of an item start edge.

FR - make time signature always visible.

[bFooz]

Bump for 6.28.