Pass server-side error messages through to the API response

[jasonwcfan]

Right now any exceptions that occur server-side are not passed through to the API response. Instead, all server-side errors return error code 500 with no additional details. This can be frustrating for errors that are easily resolved, for example expired API keys or invalid values for certain parameters.

We should pass all server-side error messages through to the API response, and use the appropriate error codes depending on the nature of the exception.

[gautamtata]

+1. Banged my head for 30 minutes before realizing that I forgot to plug the API key.

[Ayan-Bandyopadhyay]

@gautamtata which version of the python library are you on? The latest version 0.8.0 has error messages: https://pypi.org/project/psychicapi/