Add ability to define custom error handling

[omarcinkonis]

I tried to keep error handling as close as possible to the original logic, but I did make some changes:

• Error handling was not working with .then(). We were getting Axios errors. I changed to .catch(), now we throw custom errors
• Added RettiwtError (base error), ApiError, HttpError custom errors
• ApiError is handled before HttpError
• Error is handled even if error message is not defined
• Added default error message

Validation error is left unhandled (same as before). Further improvements could be made. It would be possible to return response on error without a fatal using IResponse errors

export interface IResponse<DataType> {
    data: DataType;
    errors?: IError[];
}

Everything is tested and confirmed to be working.

Please comment if you want me to make changes.

[Rishikant181]

Everything is fine except there are some minor linting errors and some changes to variable names. I'll be fixing those in a separate branch and then merging with dev.

Thanks for the contribution!