Deprecate LogUtil and redirect it's messages to slf4j logger.
Replace framework calls from LogUtil to gwt-slf4j.
Switch ManagementConsole to gwt-slf4j.
Add custom logging handlers, using a global format string (like
java.util.Logging)

Notable changes:
* Add Logging module to ErraiCommon
* Add four handlers (extending gwt-builtin handlers)
* Add ErraiSimpleFormatter (based on the java.util SimpleFormatter)
* Add StingFormat utility (emulating String#format(String, Object...))
* Add class for configuring handler log levels at runtime