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.
And by this line, you are denying to overwrite all properties that are in groupingConfig (for example groupTextTpl).