Expose singleClickEdit on Column

[ghsolomon]

GridModel currently supports clicksToEdit which specifies AG Option singleClickEdit: clicksToEdit === 1. However, we do not expose a way to specify this at the column level.

For symmetry, we could support a clicksToEdit Column option; however, this is a little confusing since we really can only support values 1 or 2. At the GridModel level, we support any number, but for any value other than 1 or 2, we set the AG Option suppressClickEdit = true. This is not something we can do at the Column level, so perhaps we're better off just exposing singleClickEdit directly.