Simplify Requests error handling (Fixes #71)

[ivyleavedtoadflax]

Description

• Resolves Error handling in create command would never fire #71 which meant that all the error handling logic for different HTTP errors across all commands (not just create as described in Handle 401 and 5xx errors in endpoint list #64 and resolved in enhancement: Handle 401 and 5xx errors in endpoint list #65) would never get triggered.
• Also creates an exceptions module and abstracts the error handling logic for Requests errors into a handler function.
• Adds test_exceptions module to test functionality of the error handler.
• Note that this will supersede enhancement: Handle 401 and 5xx errors in endpoint list #65

Checklist

• Tests added
• Relevant issue mentioned
• Documentation updated

[nsorros]

In descriptions that resolve an issue, it is good to give a quick summary of the issue

[ivyleavedtoadflax]

In descriptions that resolve an issue, it is good to give a quick summary of the issue

Added to description.