Update REMS glossary

- applying users: `#{:applicant :member}` roles
- handling users: `#{:handler :reviewer :decider :past-reviewer :past-decider}` roles
- missing events: for example `#{:application.event/voted :application.event/attachments-redacted}`

Copy-paste from board note (removed old note in the process):
> `glossary.md` is missing at least category and organization