Store the originalVersion id in ConfluencePageClass

Currently, in ConfluencePageClass, we store the page id of the revision. But when rolling back a migrated page to an earlier, we lose the stable id of the page. This is because Confluence changes the page id of a page when turning it into a historical version, and the new version gets the old page id. The historical version then has a new field, originalVersionId, containing the stable page id.

originalVerionId is not set for the current revision, but it'd be easier to have it for a lot of reasons on our side. For clarity, we will name this field stableId