Upgrade logback and slf4j after logback-android released version 3.0

logback-android does not support slf4j-api 2.0 yet and the result is that no logging appears in logcat at all when upgrading slf4j-api.

The issue is known at logback-android and a fix is on the way with the author stating that he plans to release logback-android 3.0 after merging this.

!128 (merged) introduce an update with the result being that logs did not work any longer. !129 (merged) reverts the logging update of the former MR. Let's upgrade again once a new version of logback-android is available.