Break screen's dependence on PTYTask. Fix screenResizeToWidth, which conflated cells and pixels. Reduce screen's knowledge about how windows are lain out. Remove vt100screen's knowledge of NSScreen. Remove terminalIndex, which was doing the wrong thing I think. Don't set the window's width in fullscreen (but also don't have the side-effects of setting width). Don't print a screen dump when printing an empth buffer.  Remove not-too-useful kMaxLinesToScrollAtOneTime. Fix terminalScreenWidth/HeightInCells to be more accurate. Redraw screen when switching to alt grid. Fix bug where endExtends wasn't initialized. Move VT100TerminalDelegate into its own file. add testPrinting
Only set left/right margin if left/right margins are enabled. Add testBackspace.