ACCUMULO-1956 expand docs, addition/decommision of cluster nodes

Signed-off-by: Eric Newton <eric.newton@gmail.com>
Merge branch '1.4.5-SNAPSHOT' into 1.5.1-SNAPSHOT
Merge branch '1.5.1-SNAPSHOT' into 1.6.0-SNAPSHOT
Merge branch '1.6.0-SNAPSHOT'
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/accumulo