Fix conversions between pixel offsets and timestamps.
Implement vertical zoom.
Support very large vertical scroll ranges.
Keep edit cursor visual position fixed when changing zoom level.
Fix rendering of end of sheet with very deep zoom levels.
Support basic column width adjustment.
Configure a fixed set of available column widths based on font size.
Keep edit cursor visible when changing column width.
Use a buffer cache that supports limitation of memory usage.
Limit column cache size.
Fix cursor movement to a previous system.
Remove unneeded sync.
Store sheet zoom settings in the session.
Implement sheet manager for accessing sheet settings.
Use the model for accessing sheet zoom parameters.
Remove useless Qt signal.
Store sheet column width settings in the session.
Support sheet column width access in the sheet manager.
Use the model for accessing sheet column width information.
Add a higher-level sheet widget that contains the sheet area.