Add setter callbacks to all remote entity properties

Problem/Motivation

Currently it's not possible to write to certain properties of remote entities:

• created
• changed
• remote_saved
• expires
• needs_remote_save
• deleted

It would be nice if those properties could be changed using the entity wrapper as well.
That way we're able to use rules to e.g. say if something needs a remote save or when it expires.
And while this sounds like just expires / needs_remote_save need to be writeable we don't know what other cases we might not think of yet. Thus add a setter callback to all of the properties.

Proposed resolution

Add a setter callback to all those properties.

Remaining tasks

Reviews needed.

User interface changes

None.

API changes

None - well more properties are writeable but that's not necessarily an API change.