Adverse Event context additions

[julianxcarter]

Summary

Adds two new utility functions, getAdverseEventsFromContext and getAdverseEventEntriesFromContext.

New behavior

1. New additions to contextUtils make it possible to fetch AdverseEvent resources in the context bundle.
2. The FHIRAdverseEventExtractor will now only throw an error if a study is not included in its contructorArgs. Previously, an error would be thrown whenever there were no ResearchStudy resources found in context, even though it's not exactly necessary if a study is included.

Code changes

1. Two utility functions added to contextUtils.js.
2. Any errors thrown by getResearchStudiesFromContext are now logged as debug messages in FHIRAdverseEventExtractor.js, which a custom error being thrown by that Extractor if the study contructorArg isn't included either.

Testing guidance

Testing guidance will be included in the corresponding E-MEF PR.

[dmendelowitz]

Tested on the E-MEF, works as expected!