[ENH] Allow to configure an elasticsearch tribe node to be used for read opertions, granting access to different clusters

git-svn-id: file:///var/local/code.tiki.org/tikisvn/trunk@52279 b456876b-0849-0410-b77d-98878d47e9d5
[ENH] Automatically exclude non-searchable content

git-svn-id: file:///var/local/code.tiki.org/tikisvn/trunk@52280 b456876b-0849-0410-b77d-98878d47e9d5