HBASE-12674 Add permission check to getNamespaceDescriptor()
HBASE-12568 Adopt Semantic Versioning and document it in the book
HBASE-12373 Provide a command to list visibility labels (Jerry He)

Conflicts:
	hbase-server/src/test/java/org/apache/hadoop/hbase/security/visibility/TestVisibilityLabelsWithDefaultVisLabelService.java
Fix the ASCII art

Signed-off-by: stack <stack@apache.org>