Part of #5775.
* Create _internal folder certbot-nginx
* Move configurator.py to _internal
* Move constants.py to _internal
* Move display_ops.py to _internal
* Move http_01.py to _internal
* Move nginxparser.py to _internal
* Move obj.py to _internal
* Move parser_obj.py to _internal
* Move parser.py to _internal
* Update location and references for tls_configs
* exclude parser_obj from coverage