Introduction of `sui` TUI for calendaring, plus other fixes

• Introduction of sui, a graphical TUI built with the same principles as saturn. Uses the same data and databases and configuration file, and works great with Google Calendar.
• Improvement of recurring task management with Google Calendar. Not all bugs are snipped here, but the big ones are.
• midnight and noon are now valid times in the entry language.
• saturn delete can now take multiple IDs to delete at once.
• saturn notify can now accept notification icons with the --icon flag.