Place tomatoes into the Vitamix container and secure the lid. Select Variable 7. Pulse 5 to 6 times, or until tomatoes are roughly chopped, using the tamper to press the tomatoes toward the blades. In a large saucepan with a heavy bottom, add the olive oil and heat over medium low heat. Add the chopped onions and cook, stirring, until the onions are soft but not brown, about 10 minutes. Add the tomatoes (including all juice and seeds), dates, vinegar, salt, dry mustard, celery salt, garlic powder, ground cloves, and ground allspice to the onions. Stir well to combine. Bring the mixture to a boil and then reduce the heat to a simmer. Cook uncovered, stirring occasionally, until most of the liquid has evaporated, about 1 hour 15 minutes. Allow the mixture to cool for 20 minutes, then place into the Vitamix container and secure the lid. Start the blender on its lowest speed, then quickly increase to its highest speed, using the tamper to press ingredients toward the blades. Blend for 30 seconds. Pour the mixture into an airtight container and keep in the refrigerator for up to 3 weeks. Serve chilled or at room temperature.