Make http_error_code a parameter of the MergeErrorResponse constructor. It defaults to 500, the value previously hard-coded in the call to the super class constructor. This change will allow us to specify other error codes in places where 500 is not useful. Part of mpuls/issue6009

flask>=0.7
requests
py3o.template>=0.8
py3o.renderers.pyuno>=0.3
setuptools
pypdf2
six>=1.9