[WFCORE-105] Adding configuration to support Kerberos authentication using security realms.
[WFCORE-105] Addition of a KeytabService to provide populated Subjects using the defined Keytab
[WFCORE-105] Modify the KeytabService to create the JAAS configuration on starting and to return a populated Subject on demand.
[WFCORE-105] Added a <kerberos /> element for authentication.
[WFCORE-105] Enable Kerberos as an authentication mechanism for the HTTP management interface.
[WFCORE-105] Further clean up following pull request review.
Merge pull request #214 from darranl/WFCORE-105_Rebased

[WFCORE-105] Enabling Kerberos authentication over the HTTP management interface.