Decided it's relevant to entity updated_at since tags are now indexed
alongside content.
- Also fixed tags not applied on shelf.
- Also enforced proper page API update validation.
- Adds tests to cover.
For #3319Fixes#3370
- Added test cases to cover.
- Altered parsing logic to be a little less reliant on regex.
- Added new iamge repo method for creating from data.
- Added extension validation and additional type support.
- Done some cleanup of common operations within PageContent.
- Added message to API docs/method to mention image usage.
For #2700 and #2631.
- Fixed page editor default focus not working as expected due to
misnamed attribute.
- Added owned_by to relevant areas of the API including the docs.
- Made book relation on page accessible even if deleted since it could cause an issue on views, such as audit trail, when the relation is accessed when the book is deleted.
