Logging enchancements

As for now we've got too few logging operators in code, about a half of use cases are not logged at all. Moreover, some fragments use Commons Logging, otherws use SLF4J. This should be fixed and rewritten in a uniform manner. There is no need to log in the controller, but service layer should be fuly covered with logging. Please avoid trace log messages like "Method xxx started", they are pretty useless. Also choose an appropriate log level and prefer lazy composition fot log strings.