[TASK] Add syndication service interface

This change introduce a new interface for the syndication service. This
interface can be useful if the developer need to replace the default
implementation.
[TASK] Refactor Syndication service

This change introduce a new DataProviderInterface. This interface must be
used by all syndication data provider. Currently the package support only
RSS and Atom feeds.
[TASK] Do not allow inline editing in SyndicatedDocument