Keep track of line properties for image update

Konsole wasn't really keeping track of changes to line rendition
attributes, and was just always marking for update the top line of
double-height lines. This didn't account for double-width lines, changes
back to single-width single-height, and did not provide proper support for
separate rendering of the bottom of double-height lines.

The effect can be seen on vttest "Test of known bugs" (9) -> "Erase
right half of double-width lines" (8), where a line is changed from
single-width to double-width and back. The line wasn't re-rendered on
each change, as it should.

Can also be tested with:

echo -e "\e[2J\e[1;1HTEST\n"; sleep 1; echo -e "\e[1;1H\e#6\e[2;1H"