Refine error handling

[adrianz-kainos]

Some methods especially in API/Web handlers are missing error handling.
This helper method https://github.com/KainosSoftwareLtd/TechRadar/blob/master/utils/dbhelper.js#L106 also never returns errors.
In some places the callback function uses the inverse order of arguments (error, result) or (error, null). It might help to make it uniform and always return result as the first argument.