SLING-3688 Apply slightly modified patch by Amrit Verma (Thank you very much!)

- Adds configuration property to define the default home folder
- Adds support to overwrite the home folder on a per-user basis

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1605559 13f79535-47bb-0310-9956-ffa450edef68