Revert "Setup without slf4j"

This reverts commit 2f8cc84d7d783c4f2254faf07160dce5ff4b9c41.
Removed proprietary logging and upgraded slf4j-api to 1.7.2

Conflicts:
	pom.xml
	src/main/java/com/biasedbit/efflux/session/AbstractRtpSession.java
Remove missed import
Allow subclass of RtpParticipant
Convert to Netty 4 API