OAK-1805: Debugging console

Add support for piped commands and executing an OS process.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1596825 13f79535-47bb-0310-9956-ffa450edef68
OAK-1266 - documentation

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1596829 13f79535-47bb-0310-9956-ffa450edef68