Migrate to SLF4J+Logback

Hey guys. This is a huge PR. I removed all deps to log4j, including transient. Many logger calls had to be adjusted as the syntax differs between log4j and slf4j. Every Log request should now be redirected to SLF4J via its legacy bridges. All integration tests successful. Configuration via logback.xml tested as well, all parameters taking effect.

P.S.: I had issues with whitespaces, resulting in 19000+ additions/deletions. I used ?w=1 URL parameter for this PR, hope it works. Adds/Dels should be 654 and 509, changing 141 files.