create a separate method to write to existing nwbfile

[Saksham20]

The current method of dlc2nwb library: convert_h5_to_nwb does not allow:

• write subject specific information to only 1 nwbfile. It writes all subjects' (from the config file) into individual nwbfiles in a for loop.
• Does not have the option to write to an existing nwbfile.

This PR adds a method write_subject_to_nwb that solves the 2 problems above. It also modularises the code a bit.

I think this would be a good feature addition to the library: writing to an existing nwbfile is a common use case for users that write ephys/ophys data types to an nwbfile in addition to behavior DLC data.

We are currently developing a tool (nwbconversion tools) to write various data formats to nwb. With this added feature, we can leverage this library directly.

[bendichter]

@jeylau and @AlexEMG, would you have availability to review this PR? We are trying to incorporate this library into NWB Conversion Tools, allowing us to easily compose conversion programs to NWB that include DLC data. In order to do this, we need to be able to write pose estimation data to an existing NWB file. This PR allows us to do that. Happy to answer any questions.

[h-mayorquin]

@jeylau and @AlexEMG, any chance we could some feedback on this? Is there anything we could do to help you move this forward?

[jeylau]

Sorry guys for the (very long) delay, but the PR looks great! Thanks a lot @Saksham20 for the effort you put into it!

[jeylau]

The tests fail though; could you please edit _get_pes_args to take (config_file, h5file, individual_name) in that order?

[h-mayorquin]

@jeylau Thanks for writing those suggestions. Let us know if anything else is needed.

[jeylau]

All good @h-mayorquin, thank you very much!