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.

Even if random chars are all 0, at least the first one isn't
so we know we can't return INVALID_UUID.

Admin aborts by sending an error packet for each request.
Without this, the neoctl would wait forever.

This fixes admin not always forwarding error packets from master to neoctl.

This is required, for example, for simultaneous reciprocal replication
between 2 storages.

Also, make it call _parse to simplify subclasses.

For example, with test2Clusters:

Traceback (most recent call last):
  File "neo/master/app.py", line 111, in run
    self._run()
  File "neo/master/app.py", line 131, in _run
    self.playPrimaryRole()
  File "neo/master/app.py", line 318, in playPrimaryRole
    self.provideService()
  File "neo/master/app.py", line 269, in provideService
    em.poll(1)
  File "neo/lib/event.py", line 90, in poll
    self._poll(timeout=timeout)
  File "neo/tests/threaded/__init__.py", line 150, in _poll
    Serialized.tic(self._lock)
  File "neo/tests/threaded/__init__.py", line 102, in tic
    cls.release(lock); cls.acquire(lock)
  File "neo/tests/threaded/__init__.py", line 88, in acquire
    elif threading.currentThread() in cls.pending:
TypeError: argument of type 'int' is not iterable

This commit is similar to 900d4908.

This fixes commit d90c5b83
("Allow NEO to store empty values").

This optimizes storage layout on disk, because more recent entries are often
being accessed more.

This will also simplify implementation of incremental backups.

Storage API is changed so that backends are not forced to use the checksum to
index data.