fix: set correctly request->session

The session cookie was not created because request->session pointed at
a temporary session.

While here:
- do some cleaning in App
- set request->mount too
- add fcgi_cannot_create_request_delay to the config
- fix: in mailregister plugin get model_connector from env (and not from the request)

winixd/core/config.h

@@ -180,6 +180,12 @@ public:
 	// default: 100
 	int fcgi_socket_listen;
 
+	// in order to read a request we need to properly initialize a FastCGI structure by
+	// using FCGX_InitRequest function, if FCGX_InitRequest fails then we wait fcgi_cannot_create_request_delay
+	// seconds and trying again
+	// default: 3
+	size_t fcgi_cannot_create_request_delay;
+
 	std::wstring templates_dir;
 	std::wstring templates_dir_default; // html templates from winix