loggers

- ADD: can define if a logger runs thread safe or not
- CHG: remove Facade part in names of implemented loggers
logger framework

- ADD: Id, Contrext, Principal and Thread properties to ILogMessage
- FIX: made AggregateLogger and DelegateLogger thread-safe
- ADD: started to implement XML file based logger
- FIX: added missing documentation
- FIX: null exceptions