Change the current saving policy to ignore formatting changes

With this change the old saving policy (which is our "reference here") 
will detect if a model needs to be saved by loading the filesystem
version, reserializing it in memory and compare this serialization with
the serialization of the one in the one in the resourceset.

This is necessary to avoid re-serializing because of changes of
serialization options like LINE_DELIMITER.

This is in no way something which should get commited on master and
shipped, this is only use to compare with the new implementation.
IsModifiedPolicy ignores isLoaded and use ResourceStatus

This change the IsModifiedSavingPolicy so that isLoaded is not checked
to decide whether a resource has to be saved or not. This is necessary
to keep the same behavior as the reference policy.

It also leverage the ResourceStatus.UNKNOWN to detect cases where
a resource has been added in the resourceset but has no underlying file.

Last but not least ConcurrentModifications which might happens in the
case of proxy EObjects are now avoided.