This includes an API change of Node.isIdentified, which now tells whether
identification packets have been exchanged or not.
All handlers must be updated to implement '_acceptIdentification' instead of
overriding EventHandler.acceptIdentification: this patch only does it for
StorageOperationHandler

Roughly once every 40 tries on ClusterTests.testElectionWithManyMasters I
get a "port already in use" because runner assigned two master to the same
port.

MasterHandler contains only server-side handlers.

Also, factorise code to be executed when connection is established.

Also, drop captain-obvious comments.

Also, make test_ClientConnection_writable2 test what it says it tests.

Replication is also fully reimplemented:
- It is not done anymore on whole partitions.
- It runs at lowest priority not to degrades performance for client nodes.

Schema of MySQL table is changed to optimize storage layout: rows are now
grouped by age, for good partial replication performance.
This certainly also speeds up simple loads/stores.

Cells must never be in DISCARDED state so 'getCellList' can be simplified
and all 'isUpToDate or isFeeding' can be replaced by 'not isOutOfDate'.

Commit 03ae3309 broke unit tests.

This reverts check that unneeded options are passed, and only skips run()
when used from 'neostorage' script.

Do not actually start storage node when told to reset database content.
Refuse to reset database content when non-required parameters are provided.