By Daniel Kline While Fremont Street has been adding Strip-like resort casinos, one billionaire wants to take on Caesars, MGM, Wynn, and the other big boy on the Strip. For decades downtown Las Vegas, the Fremont Street area, served as a grittier alternative the the glitz and glamour of the mega-resorts on the Las Vegas Strip. With the street closed to traffic and the massive lights and music show known as the Fremont St. Experience, not to mention the live music and DJs that take over after dark, downtown Las Vegas has become a non-stop party. The downtown casinos, at least until Circa openin…