You've probably seen by now that South Africa's first black president, Nelson Mandela, died last night. While it's clear that his legacy – including the fight for equality and his battle against racism, Aids and poverty will continue to live on, last night a stream of celebrities including Beyoncé and Cara Delevingne took to social media to mourn the loss of one of our generation's most iconic politicians/philanthropists. Here's what they posted…