Support for prescribing brand medicines

It's common for prescriptions to allow the prescriber to distinguish when the pharmacist should dispense exactly as written vs. allowing them to substitute a generic version of the medicine. For example, paper prescriptions often have two places to sign at the bottom: one to "dispense as written" and the other if they "may substitute".

There are two changes that would allow the Order Service to support the ordering of brand medications:

• Add string DrugOrder.brandName, should also add brand_name column to drug_order table
• Add boolean DrugOrder.dispenseAsWritten, should also add dispense_as_written column to drug_order table

To fully realize this functionality, it will depend on having brand names associated with drugs in the system (i.e., allowing brand name(s) to be associated with drug formulations); however, having a place for the brand name on a drug order along with a boolean to specify that the order should be dispensed as written could be used before we have the metadata in place to provide appropriate choice lists for brand names.