Changed autosave handling for better editor performance

Changed autosave handling for better editor performance

This changes how the editors interact with the parent page-editor
compontent, which handles auto-saving.
Instead of blasting the full editor content upon any change to that
parent compontent, the editors just alert of a change, without the
content. The parent compontent then requests the editor content from the
editor component when it needs that data for an autosave.

For #3981