Activities refactor

[fbacall]

Summary of changes

• Use shared partials for rendering activities to DRY up the code.
• Make sure activities can still render even if associated resources have since been deleted.
• Use i18n for activity text.
• Test each activity renders without error.

Motivation and context

Previously, each resource type had its own set of activity partials for each activity type, even though they were almost always identical to other types' partials. When a new resource type was added, often these partials were missing and would cause errors when trying to render the activity log (which was not picked up by any tests).

Checklist

• I have read and followed the CONTRIBUTING guide.
• I confirm that I have the authority necessary to make this contribution on behalf of its copyright owner and agree
  to license it to the TeSS codebase under the
  BSD license.