MOSCOW — The body of Alexei Navalny, Russian President Vladimir Putin’s most formidable critic, was lowered into the ground to the sounds of Frank Sinatra’s “My Way” as thousands of his supporters outside a cemetery chanted to be allowed in to pay their respects. Despite the mass of followers and the heavy presence of riot police, there were no major protests or clashes as Russia’s most prominent dissident was laid to rest. The opposition leader died suddenly at the age of 47 in the Polar Wolf prison colony in northern Russia — a death that his widow, Yulia Navalnaya, and other supporters have described as “murder” but which Russian authorities attributed to “natural causes.”