BibSched: speed improvements

• Use curse.erase() instead of curse.clear() to avoid repainting the whole window
• Update rows right after deleting a task so that we do not experience an annoying delay
• Fixes a bug that would allow your selected row to be past the current displayed number of rows
• Limit the display of archived to tasks to 500
• Restore stdout/stderr on exit to see tracebacks of exception when bibsched fails
• Fixes a bug that would not delete the Y/N and options panels once closed (also speeds up their closing) (closes #1053)