Template python3_django - wrong nginx locations for static files

[matthieumarrast]

While creating a mfserv plugin using python3_django template on metwork v1.x, the app section in the config.ini file is named [app_main] whereas the main app of a django project is the name of the project (i.e the plugin name). Note that in last metwork version (0.X) the app section was named [app_<app_django>].
It causes nginx location to be /<plugin_name>/main/ instead of /<plugin_name>/<app_django>/ which is the expected value as per the default path defined in postinstall script for the static files.

[thebaptiste]

Closed by #529