Vasopressor agg

[alistairewj]

Creates useful aggregations of vasoactive agents

• added milrinone as another medication
• vasoactive_agent table has vasopressors/inotrope doses together, merging overlapping start/stop times as needed
• norepinephrine_equivalent_dose calculates an equivalent total dose from multiple ongoing agents
• updated make_concepts to generate these tables in the right order - and refactored it to be less repetitive

Unfortunately I couldn't find angiotensin II or methylene blue in MetaVision, and so these queries won't capture that data for those rare patients receiving those medications.