By THÉRÈSE MARGOLIS     San Miguel de Allende will host its fourth annual edition of Dress to Give Fashion Days from Wednesday, April 25, through Friday, April 27. The multifaceted display of  fashion and art will showcase more than 20 Mexican designers, including the latest collection by the world-renowned house Piñeda Covalin, as well as up-and-coming Mexican visual artists. All of the money