Portal Dataset schema - model whether aggregate or individual-level and properties for individuals and specimens

[anngvu]

@cconrad8 After review and comparison, this would be useful and there will certainly be researchers who apply range filtering for this. This is optional attribute; there will datasets with mice or non-biological or otherwise not applicable where this will be null and simply won't show up in the card. On the other hand, specimens can still be applied for non-biological data.