Renders as markup the specified column value of the table header into the specified element, usually as a text node.
Default implementation delegates to the default {@link org.itsnat.core.domutil.ElementRenderer}.
Default implementation ignores isSelected and hasFocus (current implementation of ItsNat tables does not handle focus on table header columns, ever is false).
@param tableHeader the table header component, may be used to provide contextual information. Default implementation ignores it.
@param column the column index.
@param value the value to render.
@param isSelected true if the column is selected.
@param hasFocus true if the column has the focus.
@param columnContentElem the table column content element to render the value into.Is a hint, if provided should be obtained by calling
tableHeader.getItsNatTableHeaderUI().getColumnContentElementAt(column).
@param isNew true if this is the first time the markup is rendered. Default implementation ignores this parameter.