Revise error types (warning or notice) raised by system

We are currently reporting around 100 custom error messages, that will help developers to take care of possible problems before they happen. We should set proper error message type for each of them using following logic:

• notice - information stuff, should be fixed, but not top priority and doesn't affect system's stability
• warning - possible cause for larger problem, must be fixed before project is shown to client
• fatal - critical, application failure and must not exist at all at any of development stages