QPID-5138: Add improvements and fixes into Web Management Console preferences:
           Use UTC time zone by default if no time zone is set
           Create preferences dialog on demand
           Enable preferences Set buttons only when changes are made
           Display log viewer last update time for preferred and browser time zones
           Fix provider name editing

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1531965 13f79535-47bb-0310-9956-ffa450edef68