Improve performance on Windows

[andythigpen]

Performance on Windows is terrible right now.

[andythigpen]

Removing the pixmap painter in the terminal's paintEvent handler will help.

[andythigpen]

Also need to improve performance when scrolling in normal buffer, right now flickering occurs.

[andythigpen]

Removed pixmap code, as it doesn't work as intended.

Closed by ebc4a37

[andythigpen]

Investigate - Instead of waiting until end of data block, mark entire screen dirty on scroll to improve performance on scrolling in normal buffer