With one of Austin's largest venture capital rounds of 2017 under its belt and thousands of real estate agents on its platform, Opcity Inc. has a new headquarters to accommodate its substantial growth — with room to expand as that trajectory continues upward. The real estate technology company this week moved into 50,000 square feet at 6800 Burleson Road, an industrial pocket of Southeast Austin near the MetCenter redevelopment and Austin-Bergstrom International Airport. The Opcity building is…