Traceback swallowed by error handling code

[coltonlw]

dispatcher method in api.py does not log traceback when it catches an error that is not an instance of webapp2.HTTPException
https://github.com/scitran/core/blob/master/api/api.py#L200
Suggest removing this except block, causing the error to be handled by WSGIApplication._internal_error. Since _internal_error does not log a traceback with the exception, we need to add an error handler for code 500 to log the traceback and then return webob.exc.HTTPInternalServerError which is the same return value as _internal_error. This is better than adding code to log the traceback in the dispatcher function of our router, since any exceptions thrown outside of the router code will also be logged

[coltonlw]

This should be coordinated with #199 so that the traceback is logged to the request specific logger adapter. Then when we get a traceback and a 500, we'll have contextual request info to aid in debugging.

[coltonlw]

fixed by #482