Added core facing convenience logging functions

Many parts of the core need to issue a message here and there, many of these even created their own local convenience functions to do it, so as to avoid instantiating a Message() and selecting a MessageType redundantly.

This patch adds some convenience functions to the Messenger and updates the core to call these functions directly, removing any duplicated _message() functions and using the Messenger available to the core components directly.

This also updates Messenger to be fully type annotated as per pep484.