BANGKOK — Thaksin Shinawatra, the billionaire former prime minister of Thailand, made a dramatic return home after more than a decade of self-imposed exile. In 2011, Thaksin’s sister Yingluck Shinawatra led the Pheu Thai party to an landslide election victory. Thaksin’s desire to return home seemed finally possible as Thais last year headed to a general election in which the …