Having trouble distinguishing a Thor from a Thanos as you head to the theater for “Avengers: Age of Ultron”? Unless you grew up sleeping in Captain America underoos or have the IQ of Tony Stark, the expanding Marvel movie mythos could be hard to keep straight. So to help make small talk at your next cocktail party — a very nerdy cocktail party — here’s the Daily News’ handy primer to ready you for the “Avengers” sequel, out Friday: ‘AVENGERS: AGE OF ULTRON’ STARS GIVE BEHIND-THE-SCENES LOOK AT SUPER SEQUEL REVIEW: ‘AGE OF ULTRON’ IS HIGH-OCTANE THRILLRIDE The Story So Far After thwarting an alien invasion at the end of the first “Avengers,” the superhero teammates scattered in different directions for their own adventures … except poor Hawkeye (Jeremy Renner), who wasn’t invited to “Iron Man 3,” “Thor: The Dark World” or “Captain America: The Winter Soldier.” Heck, he didn’t even get a cameo on ABC TV series “Marvel’s Agents of S.H.I.E.L.D.” During his last solo outing in “Iron Man 3,” Tony Stark (Robert Downey Jr.) created a legion of robotic Iron Men — an initiative that seems to have enabled him to dabble in the more potentially dangerous area…