Improve Monolog and Symfony Compatibility

Implementing a custom Monolog logger (rather than the one packaged with Silex) along with Silex's [bootstrappable](http://silex.sensiolabs.org/doc/usage.html#bootstrap) [debug mode](http://silex.sensiolabs.org/doc/usage.html#error-handlers) causes conflicts. (In many cases, only the browser will display the error, or Monolog will handle the error and exit before the browser can display details.)

We have this issue worked out. However, Monolog is still logging Symfony's DummyException (which is part of the Silex debug mode flow) rather than the real exception. This provides helpful info, but it would be better to provide more pertinent context.