Find better user-facing term to replace "Entity" and "Parent entity"

[danicahelb]

Related to VEuPathDB/EdaNewIssues#287 and VEuPathDB/EdaDataService#180; revisit verbiage post-b58

Possible suggestions to use instead of “entity”:

• “Observational unit” (see: https://cran.r-project.org/web/packages/tidyr/vignettes/tidy-data.html)
• “Type”
• “Group”