EXCLUSIVE: First the abolitionist leader Harriet Ross Tubman pushed the controversial President (and Native American foe) Andrew Jackson off the $20 bill to become the first African American on U.S. currency, and now she’s getting her own feature film. It seems quite appropriate that Charles D. King, who was the first and only African American to rise from the mailroom to partner in the 118-year history of WME, is one of the producers leading the charge on the new film…