Fix multiple z device ingestion in prairieviewreader.py

[kushalbakshi]

This PR addresses issue #77.

The updated code was used to ingest 3 different versions of .xml metadata files into the ScanInfo and ScanInfo.Field tables from DataJoint Element Calcium Imaging. Version 1 and 2 contained two z-axis controllers at different "subindex" locations in the .xml file. Version 3 contained only 1 z-axis coordinate which did not change during the acquisition. All 3 ingestions completed without errors and populated all the attributes correctly.

In this PR I perform the following:

• Update code to handle multiple z-devices in PrairieView's .xml metadata file
• Test the code to verify ingestion runs successfully for the user who created the issue
• Test the code to verify ingestion runs successfully for other versions of .xml files available to me as of this PR.
• Attach screenshots of successful ingestion of ScanInfo and ScanInfo.Field
• Update CHANGELOG
• Update version.py

Screenshot of test schema ingestion:

[kabilar]

@kushalbakshi Thanks for the joint coding session today. We are close to merging. We just need to handle the case when the same z depth is used by both controllers.

[kabilar]

Thanks @kushalbakshi!