Model for stock that is not live in stockcenter

[ypandit]

• All the stock (strains/plasmids) present in the stock center fall in stockcollection => 'Dicty StockCenter'
• There are plasmids that are linked to strains, but need not be in the stockcenter. Ref: #63
  • In the future, these plasmids may/may not be in the stockcenter
• These plasmids should be modeled in a way similar to the ones which are in the stockcenter
  • Only difference, use stockcollection => 'Dicty Azkaban'
  • If ever, the plasmis/strain is made available in the stockcenter, change to stockcollection => 'Dicty StockCenter'