By THÉRÈSE MARGOLIS     Housed inside an unassuming art déco home in Mexico City’s recently renovated San Miguel de Chapultepec neighborhood, Padella is an unpretentious but inviting European family-style restaurant with a downhome feel and a surprisingly sophisticated menu. The décor of Padella is understated, with each of the restaurant’s intimate dining rooms decorated in shades of green, blue and gray, with bits of