Implement compacting values from not exists nodes

[negasus]

Save memory proposal.

If many nodes leaved cluster (and possible joined to cluster with new ID), its values with old IDs will be take memory forever.

Consider compacting proccess for orphans values to one virtual node value.

For example. Node2 and greater are orphans

Var1:
node1: 100
node2: 200
node3: 300
node4: 400

After compacting

Var1:
node1: 200
SpecialVirtualNode: 200+300+400