Update modx.grid.js

When you enable grouping on a MODx.grid.Grid, it will apply a Ext.grid.GroupingView to the grid, which is great feature, but as I want to hide/disable the "group by this column" feature when you click on the little arrow near each column header, I need to pass "enableGroupingMenu: false" to the GroupingView. But I cannot do that (whithout touching the core files).

Maybe good to have a "groupingConfig: { }" which will be passed when you set this up in your grid. This is how it works for me.
the var groupingConfig is what MODX currently passes to the GroupingView and the config.groupingConfig is what you can pass extra via the grid setup. When you change the order you cannot overwrite the MODX settings. I'd like to be as flexible as can be.. that's why I did it this order.