v6.0.0-M1

Change log:

cfae849 [artifactory-release] Release version 6.0.0-M1
d6bf681 Upgrade dependencies; prepare for release
c28e251 Fix ControlBusTests for DefaultHeaderChannelReg
8e7a0a0 Add checkClasspathForConflicts Gradle task
6ebdd4f Upgrade Dokka plugin to 1.6.10
439d741 Upgrade to H2 2.0.206
b3ae24e Fixes according latest upgrades
a80b226 Start 6.0 version