added method in dateUtils to return age as float value rather than just strings
added method for getting all patient ages
created ResearchItem class, this is meant to serve as a common data model for all research data requests.
trying to create unified data model for research items. need to revisit and reeval structure of ResearchItem class.
added median, average and range calculations. they will need to be seperated into service layer.
added gender lookup to research service
Merge branch 'research-service' of https://github.com/unfixed/femr into feature-graph
Added tooltip to line graph