Improve how the page status is informed to users

[leandrocp]

The Page tab on the page editor represents the draft version of the page while the Revisions tab shows all the published versions, but that distinction between "draft" and "published" (the status) is not very clear which may cause some confusion.

A potential improvement is to display on the Page tab whether that version is equal the latest published version or display the diff so we can essentially tell users "this page is synced/updated or this page has some unpublished (draft) changes)" and then display such changes so the person working on it or someone else know what changes we're not published yet.

Depends on #229