Support developer consistency across OS/ Windows

[helen-m-lin]

Is your feature request related to a problem? Please describe.
As a developer, I want to be able to run the unit tests and have the same experience on Windows compared to if I develop on Linux.

Describe the solution you'd like
Some issues with unit tests have already been resolved in previous PR #62 for path comparisons.

One remaining issue is that the error messages displayed from /api/validate_csv are slightly different depending on OS, which breaks the unit tests if running on Windows. We can pull out the error message text returned by /api/validate_csv using e.Exception or other format rather than directly returning repre(e), and update all unit tests affected.

Example:
Currently expected on Linux: "AttributeError('WRONG_MODALITY_HERE')"
Current expected on Windows: "AttributeError(\"type object 'Modality' has no attribute 'WRONG_MODALITY_HERE'\")"

We should check if there are any other issues related for running on different OS.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

[jtyoung84]

@jtyoung84 Create a user story for this

[jtyoung84]

Closed by #66