Convert a scarlet blend into a persistable data object
- Parameters:
- 
- blendscarlet.Blend
- The blend that is being persisted. 
- psfCentertupleofint
- The center of the PSF. 
- xy0tupleofint
- The lower coordinate of the entire blend. 
 
- Returns:
- 
- blendDataScarletBlendDataModel
- The data model for a single blend.