Add NWBIO

[apdavison]

This PR adds NWBIO, an IO module for reading and writing the Neurodata Without Borders format (cf #221).

This is a work in progress, which doesn't support all possible contents of an NWB file, but I think it is good enough for people to try it, and let us know (by commenting here) what doesn't work, or could be done better. Many thanks to @legouee for her work on this.

TODO

• write Block, Segment, Epoch, Event, AnalogSignal, IrregularlySampledSignal, SpikeTrain using base TimeSeries
• write Unit, ChannelIndex (or whatever replaces them)
• write ImageSequence and related
• allow user to choose where to write data (e.g. "acquisition", "stimulus", "analysis") by providing guiding annotations
• allow user to write subclasses of TimeSeries by providing guiding annotations
• read "acquisition" and "stimulus" groups
• read metadata associated with processing modules and make it available through annotations
• support array annotations

Usage example: https://github.com/apdavison/python-neo/blob/nwb2/examples/NWB-Allen-Institute-Example.ipynb

[JuliaSprenger]

@apdavison @legouee I think we can merge this PR soon to have a first version of the NWBIO in the next release. The most important change requests for this would be the incorporation of some testfiles also on gin (if you have some, as we can then tag the release to a fixed version of the test files), the incorporation of the BaseTests and some completion that is still lacking on the docstrings. Also I am not sure about some of the discussions in this thread form the end of last year, if there are outdated, could you resolve them?

[JuliaSprenger]

@legouee @apdavison The test file is now on gin. Can you include it in the set of files used by the unittests and also include the common rawio tests by inheriting from BaseTestIO?

[samuelgarcia]

@JuliaSprenger : since it now use BaseTestIO for tests, I think we can merge no ?

[samuelgarcia]

There are some warning in test_nwb.py
I guess we can live with then for a while.

[JuliaSprenger]

@apdavison @legouee I cleaned all open comments, moved unresolved ones to #1013 for the future. I fixed the layout to be pep8 compatible and fixed some docstrings / typos. Under the assumption that you don't plan to include apdavison#6 here any more I would be ok to merge the current version and fix the remaining issues listed in #1013 in the next release.