Expose Enable/Disable explore for datasets through Router

Bamboo : https://builds.cask.co/browse/CDAP-RBT50
You shouldn't have to create another ``AbstractExploreClient``. You can use here the ``FixedAddressExploreClient``. You will have to remove the overridden methods ``enableExploreDataset`` and ``disableExploreDataset``, which make this class not support those operations.