Hard-coded tissue/treatment terms in biomaterial

[spficklin]

The sep__biological_sample field has hardocded to pull the attributes 'treatment' and 'tissue' for all biomaterials. It includes these in the browser as shown in the screenshot below. The problem is that not all biomaterials will have these fields. It seems many of the BioSamples from NCBI don't have them. I think rather than hard-coding those attributes that the field should have an admin feature that let's the site admin choose which attributes to include in the table. That gives more flexibility.