Add Features from cwohlman fork

[cwohlman]

On my fork I've added numerous features to the kogrid:

• Added grouped rows and aggregation
• Add a footer row which will show totals for each column
• Improve the naming of the group column
• Support for sorting grouped grids
• Create Expand/Collapse-all buttons
• Improve speed of grouped grid, esp when expanding and collapsing rows
• Add an amd module output to the build process
• Add cell selection and improve row selection

To see the grid in action please see the example page

I'd like to see these features available to everyone else using the kogrid.