small cleanup
removed mockit until it really be needed.
ZkConnection: using ListenableFutures. Using separate ExecutorServices (by default same thread) to resubmit operations.
extracted ZKAgreementsStorage, buckets implemented.
format pom.xml and add mockito
ZkAgreementStorage tests
adding precheck for submitProposal
fixing tests for new buckets system (number of agreements can be greate then expected)