Handle editable grid cell change events.

Send the changed value to the underlying Cursor.
Rename onRowCountChange to handleRowCountChange.

For consistency with other event handlers.
Rename onRowCountChange to handleRowCountChange.

For consistency with other event handlers.
Send a CURSOR_MOVED event to Grid when Cursor moves.
Handle cursor's BEFORE_DISCARD by prompting user with a dialog.
Improve docs for RowCountChange and add missing semicolon.
Eliminate wasteful Grid refreshes on null scrolling.

Fix row refresh when scrolled (grid/data index confusion bug).