Use a custom QuickTip instance separate from the main QuickTips singleton, so that we
can give it a custom frame style. Responds to errorqtip rather than the qtip property.
@static
function() {
            var tip = this.tip;
            if (!tip) {
                tip = this.tip = Ext.create('Ext.tip.QuickTip', {
                    ui: 'form-invalid'
                });
                tip.tagConfig = Ext.apply({}, {attribute: 'errorqtip'}, tip.tagConfig);
            }
        }