Sets glyph that provides the icon image for this header.  This method will replace any existing
glyph if one has already been set.
@param {Number/String} glyph the numeric charCode or string charCode/font-family.
This parameter expects a format consistent with that of {@link #glyph}
function(glyph) {
        var me = this,
            iconCmp = me.iconCmp;
        
        if (!me.iconCmp) {
            me.initIconCmp();
            me.insert(0, me.iconCmp);
        } else if (iconCmp) {
            if (glyph) {
                me.iconCmp.setGlyph(glyph);
            } else {
                me.iconCmp.destroy();
                delete me.iconCmp;
            }
        }
    }