[LOGBACK-1114] Migrate from fest-assert to assertj

fest-assert is a defunct library which was replaced by assertj.

migration notes here.

http://joel-costigliola.github.io/assertj/assertj-core-migrating-from-fest.html#fest-1.4

Merge remote-tracking branch 'abatkin/access_pattern_conversions' into abatkin-access_pattern_conversions

Conflicts (resolved):
	logback-access/src/main/java/ch/qos/logback/access/PatternLayout.java
	logback-access/src/main/java/ch/qos/logback/access/spi/AccessEvent.java
	logback-access/src/main/java/ch/qos/logback/access/spi/IAccessEvent.java
	logback-access/src/main/java/ch/qos/logback/access/tomcat/LogbackValve.java