Disable messages panel and toggle

Disables the messages toggle in header toolbar and side-panel.  Questionable value and current design causes some contention, so lets turn it off until we can design/impl something proper here.

FTR messages still show up, but no longer can see history in the UI... except in the ?debug mode.

Related to:
* https://issues.sonatype.org/browse/NEXUS-7643
* https://issues.sonatype.org/browse/NEXUS-6804
* https://issues.sonatype.org/browse/NEXUS-7321
* https://issues.sonatype.org/browse/NEXUS-7347