GDA-5000 Switch to SLF4J 1.7.5
GDA-5000 / GDA-5780 Switch uk.ac.gda.common to Logback 1.1.0

Update LogbackUtils & LogbackUtilsTest following introduction of
ILoggingEvent interface
GDA-5769 uk.ac.gda.libs: change com.springsource.slf4j.org.apache.commons.logging dependency to jcl.over.slf4j