Make error page nice

This stops the error page from being a blank white screen, and also logs qiita_pet errors to our qiita logger for later handling.
Seems odd to me that it's always only a Runtime error, but maybe I'm not understanding something.  I can see why it's always a runtime error -- since the error is raised when the application is running -- but when would it be a critical error?  Is it not possible to have a critical runtime error?