Allow LoggerAdapter or custom libraries to call bugsnag.notify without breaking grouping

This fixes an issue where custom logging libraries, e.g. a LoggerAdapter would cause incorrect grouping in bugsnag.  If you look at notification.py before these changes, you'll see that it's excluding python's logging library and the bugsnag library from tracebacks.  Without this, every event is recorded as the same bug in bugsnag, because the last line of the TB is the same.  If you decide to wrap the BugsnagHandler or otherwise create your own library that calls bugsnag.notify(), you will see this same issue because the last line of traceback will be the line in your library that calls bugsnag.notifty().  This PR allows you to specify a configuration of modules that should also be excluded from tracebacks.  You can then put your custom logging code in something like mypackage.logging, and add that to traceback_exclude_modules.  This list must be actual objects of type module, not module name strings.