org/jtalks/jcommune/service/nontransactional/SecurityServiceImpl.java: use placeholders from slf4j

(Initially created as http://fisheye.jtalks.org/cru/JC-45 but I don't know it is visible for all or not, so I create this ticket.)

One idea about this line: https://github.com/jtalks-org/jtalks/commit/c9eefeef9ebd0b97e40c390824c107e7171ff6c5#L1R174

If we are using slf4j so why not use placeholders which made code more readable and faster in some circumstances?

So, instead of

>logger.debug("Deleted securedObject " + clazz + " with id: " + id);

I suggest to write

>logger.debug("Deleted securedObject {} with id: {}", clazz, id);

See http://www.slf4j.org/faq.html#logging_performance

(Also, this probably should me changed in all source base.)