By Shivam Patel and Sudipto Ganguly NEW DELHI (Reuters) -Students were detained by the Delhi police on Wednesday as they gathered to watch a recent BBC documentary about Prime Minister Narendra Modi that India has dismissed as propaganda and blocked its streaming and sharing on social media. This follows similar disruptions, some of which turned violent, at gatherings this week by students to watch the documentary that questions Modi’s leadership during deadly riots two decades ago, as his opponents raise questions of government censorship. Modi, who is aiming for a third term in elections nex…