ALICIA POWELL CELLIST Yo-Yo Ma and pianist Kathryn Stott have teamed up for the third time in "Songs of Comfort and Hope," dedicated to all the people who are going through tough times around the world. The album, coming out on Friday, starts by acknowledging the Black Lives Matter movement with "Ol' Man River." Other tracks include "Somewhere Over the Rainbow," "Moscow Nights," "Waltzing Matilda," and the South African lullaby, "Thula Baba." "All of these songs have specific meaning for people in different places," Ma said, noting that the coronavirus pandemic had been a global experience. "We're hoping that this…