One by one, members of Iraq's minority Yazidi community light oil lamps to mark their New Year at a sacred shrine, but for Omar Sinan the celebration cannot erase the atrocities of jihadist rule.In 2014, the Islamic State (IS) group swept across swathes of Iraq, carrying out horrific violence against the Kurdish-speaking community whose non-Muslim faith the extremists considered heretical.IS massacred thousands of men and abducted thousands of women and girls as sex slaves.