Add support for unhandled version conflict to Page List

[malinajirka]

Expected behavior

When the user edits a post in offline and edits the same post in remote a version conflict is created. The app should display "Version conflict" label as soon as it detects the conflict. It should show a conflict resolution dialog when the user clicks on the item.

Actual behavior

The app just ignores the conflict and pushes any changes to the server.

This feature is already implemented in PostList.

Note: We will probably need to check if the page has conflict here. And show the version conflict label + show conflict resolution dialog when the user clicks on the page item.