“The Gilded Age” returns for a second (and possibly final) season that feels even more conspicuously like “Downton Abbey Lite.” That’s not necessarily bad, as the show remains highly watchable as a finely tailored, lushly decorated soap, with the added benefit of incorporating 19th-century history, like early struggles of the labor movement (timely, given Hollywood’s recent woes) and the opening of the Brooklyn Bridge.