It was freezing outside, but the 60-odd Chinatown community activists gathered in front of Gracie Mansion yesterday were fired up. In English, Spanish and Chinese, they decried Mayor de Blasio’s rezoning plan and ties to the real estate industry, flinging insults and calling for his resignation.  “Coward!” “Racist!” “Shame!” they yelled. As the sun set, they even left him with a “gift.”