Should be possible to show cellMenu manually

[chuckn0rris]

Forum post

We have public showContextMenu but in real it's too complex task to collect all required data for event param to show context menu.
It requires columnId, cellSelector, DOM event, record itself, etc, but in docs it called just event.

Add showContextMenuFor(cell) method with easy to understand params list. We have showContextMenuFor for eventMenu feature, that requires only record as param.