This is an implementation of the changes I suggested in #6813: separating logging and exception handling.

I'm opening it as a separate pull request so that we can discuss it here (wether we want this or not) and I can post screenshots without flooding the other pull request.

Summary

• serious errors and uncatched exceptions are not handled by the logger anymore (because they are errors which stop the page, this is not logging, this is error handling)
• the error handler logs warnings and notices into the logger, and turns errors into exceptions (ErrorException)
• the exception handler catches all uncatched exceptions (including ErrorException) and display them to the user (HTML or CLI)
• the "screen" backend now logs message in HTML notification boxes (using the Notification class): it doesn't hijack/break HTML/JSON output anymore
• I've normalized exceptions/errors shown to the user in HTML (wether they are catched by the FrontController or not)

Screenshots

Uncatched exception in a controller/API/…

Same as before:

Uncatched exception outside of the dispatch loop

Before:

Now:

Error

Was:

Now looks like this:

Fatal error

Same as before:

Custom message logged when screen logging is enabled

Example code:

Log::warning('This is a warning');
Log::error('This is an error');

Before:

(the lines of log where added at the top of the page)

Now:

(we use the notification API)