Add sorting to DataGrid; handle duplicate combo and other fixes

[errael]

Three commits

• Add a "sorter" to the SSDataGrid #7 Swing's column sorting added to DataGrid; interactions with insert row.
• SSDataGrid ComboBox Issue with duplicate entries #126 Use SimpleComboModel so duplicate names in combo selector are unique.
• When clicking on column, cycle through unsorted. Fix hideColumns(). Simplify getSelectedColumns().

Try this stuff using Example5.

This PR fixes primary issues. It does not handle the 4.x specific stuff like #12 and #8. Or new features like filtering #127, or #6 or #9. But note that Swing's sorting includes filtering capability, need an SS API.

open questions to consider during review

• What kind of handling is required by Grid's ComboBox for null and/or unknown values coming from the database? I think getCellEditorValue() does the same thing, but I think the old behavior was inconsistent when getSelectedIndex() was -1.
• Throw if SSDataGrid.setModel() and currently has a SSTableModel?
• Note change to Control-X handling (my use of Ctrl-X was broken).
• Don't give SSTableModel a JTable.
• Why is there SSDataGrid.tableModel?
• There's arrays in API, convert them to List<>.
• What is the messageWindow all about?
• The hidden columns array shows up in both table and model.
• Why rowCount/columnCount variables in both grid/model?
• There's a bunch of TODOs added, comments appreciated.