On Thursday night, “Nashville” returns on CMT for its fifth season – or maybe more accurately, “Nashville 2.0.” The soapy country music drama has a new network after ABC gave it the boot in May, and new executive producers Marshall Herskovitz and Ed Zwick have taken over showrunner duties. Recently, I re-watched the first four seasons of “Nashville” and was surprised at how much I learned about the show, which took some bizarre, enraging and convoluted turns.