[NixIO] duplicate naming issue with array_annotations

[rgutzen]

When reading a neo object with array annotations and writing it back with the NixIO, the array annotation causes the error:
DuplicateName: Duplicate name - names have to be unique for a given entity type & parent. (create_property)

Here a minimal code example:

import neo
import quantities as pq
import numpy as np

asig = neo.AnalogSignal(signal=np.array([[1,2,3,4,5], [6,7,8,9,10]]),
                        units='dimensionless',
                        sampling_rate=1*pq.Hz,
                        array_annotations={'labels': ['a','b','c','d','e']})

block = neo.Block()
seg = neo.Segment()
block.segments.append(seg)
block.segments[0].analogsignals.append(asig)

with neo.NixIO('temp.nix') as io:
    io.write(block)
with neo.NixIO('temp.nix') as io:
    loaded_block = io.read_block()
with neo.NixIO('temp2.nix') as io:
    io.write(loaded_block)

neo v0.8.0
nixio v1.5.0b1