Created RunAs class to execute Runnable and Callable with the security context of a particular User

git-svn-id: svn://svn.openvpms.org/openvpms/framework/branches/1.8-dev@6289 9e4fa352-aafb-0310-9071-df624684024b
Added ArchetypeQueryHelper.getNameIMObjectReference, IArchetypeService)

git-svn-id: svn://svn.openvpms.org/openvpms/framework/branches/1.8-dev@6291 9e4fa352-aafb-0310-9071-df624684024b