Activity feed: Summary of changes in comparisons and version views

[chillu]

Overview

As a content author working in a multi author CMS, I can review changes made by myself and other authors when viewing older versions of a record

Design reference: https://projects.invisionapp.com/dsm/silver-stripe/silver-stripe/folder/components/5c68f96ffb26bb0018525d20

Acceptance Criteria

• When viewing a version of a record, changes to owned relationships made as part of this version/snapshot are listed
• When comparing two versions of a record, changes to owned relationships between those versions are listed
• Works with any versioned records that support the existing versioned viewer
• Informs me when there's no changes on owned relationships (only direct changes to the record)

Notes

• The format of the summary should be the same as summary of changes in editing context
• It's unclear if we should allow comparing snapshots with other snapshots, since there might be no changes on the record itself (only the owned relationships)
• Should be lazy loaded to avoid slowing down version viewing
• Out of scope: Nested diff views