Generalize error handling

[revolko]

Let's create kind of generic way to handle errors.

Errors can happen either in subscriber or publisher layer. Because of that I will differentiate errors to two groups:

• subscriber error
  • Error happened during handle of incoming data (handle of notification)
  • e.g.: unknown message/unexpected columns/missing table...
• publisher error
  • Error happened while saving data to target
  • e.g.: target not available/query execution error (or timeout)...