New visible column does not set "selected" style on selected rows. #56

How to reproduce:

• Define the grid with some hidden columns (visible: false).
• Select a few rows.
• Turn all columns "visible" and set them by calling:

_datagrid.setColumns(allVisibleColumns); // Where 'allVisibleColumns' are visible = true

The Problem:

Newly visible columns with selected rows are missing the 'selected' css rule. So their background never shows as 'selected'.