This year, the Boston Symphony Orchestra is celebrating the 100th birthday of the late György Ligeti, one of the 20th century’s most influential and legendary composers. As part of the festivities, the BSO will be performing a free concert series this week, highlighting Ligeti’s innovation and musical impact. Among those conducting and performing the Ligeti 100 Festival is acclaimed British composer, pianist and former BSO artistic partner Thomas Adès. GBH’s All Things Considered host Arun Rath spoke…