[TASK] adopt specced error types and status codes

and some cleanup
[FEATURE] add error types

- NotFoundError
- TimeOutError

add error and response handler logic to support these types
[FEATURE] finish response handling for payments class
[TASK] follow express deprecation suggestions

for part of the app that has been updated with response handling so far
Merge pull request #131 from geertweening/develop

[FEATURE] response and error handling