Add local time information to the meta-data tables and introduce snapshot notification server

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Introduce local DC timestamp information into meta_data ets tables.
The main use-case - get notified when particular transaction is fully
replicated to the local DC, as it may be spread across multiple partitions
that reside on multiple nodes. The change should not affect the behaviour
of dc_utilities:get_stable_snapshot/0.

Meta data notification server is added to antidote application, to provide
trivial notification subscription system, for subsystems which are interested
to get notified when particular snapshot is fully replicated in the local DC.
Such a service has an update lag, which is equal to periodic timer in
meta_data_sender

vector_orddict is extended to support append operation, and similar to behaviour
of dict:append.

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Hi, just kind reminder regarding this PR @bieniusa Please let me know if you intend to review it.

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Closed this in favor of https://github.com/vaxine-io/vaxine/pull/44 Added changes requested in this PR