[sync] new sync types: UPDATE|REFRESH from CLIENT|SERVER

[Karsten Fourmont]

Hi,

thanks to the refactoring and the test case, new features are now way 
easier to implement.

I just added support for 4 missing sync types:

1) ONE_WAY_FROM_CLIENT
2) REFRESH_FROM_CLIENT

3) ONE_WAY_FROM_SERVER
4) REFRESH_FROM_SERVER

the first two: only the client sends to the server. client remains 
unchanged.
the last two: only the server sends to the client. server remains unchanged.

the one_way_* are delta syncs while the refresh* do a trasnfer of the 
complete data set.

The synthesis client supports these.

After a quick glance it seems to work fine, but it's not thoroughly 
tested yet.

Cheers,
  Karsten