Removed useless readonly property on some fields

Add master = true to uwsgi.ini

Add the custom message provided by HttpException to the template

Before when session restore fails the webui was answering "Unknown status 200" as content.
Now it produce 2 log messages (maybe)

broken nginx conf + absolute path in slim that is known only at build time

using --plugin option instead of uwsgi_python3 shortcut (can be uwsgi_python34 etc)

Adds a LODEL2LOGDIR to buildconf.py
Adds a nginx-conf option to slim
...

Now create an INSTANCE_NAME.sock in @localstatedir@/uwsgi_sockets
Note : the localstatedir is wrong -_- /usr/var instead of /var........

Using execl instead of fork to preserv the pid

SLIM is now able to edit configuration from CLI, to start instances etc.