allow to specify how many times we can try to connect to the database at startup

add config options:
db_startup_connection_max_attempts - default 0 (infinite)
db_startup_connection_attempt_delay - delay in seconds between attempts (default 5)

BREAKING CHANGE: WINIX_PLUGIN_INIT plugin message requires to set result status,
you have to set the result status to true (env.res) if your
plugin was initialized correctly, otherwise winix will not start

winixd/core/app.h

@@ -74,7 +74,8 @@ public:
 	bool DropPrivileges();
 	void InitLoggers();
 	Log & GetMainLog();
-	void InitPlugins();
+	void LoadPlugins();
+	bool InitializePlugins();
 	bool Init();
 	void Start();
 	void Close();
@@ -188,6 +189,8 @@ private:
 	// file logger, one object for all Log objects
 	FileLog file_log;
 
+	bool AddSystemThreads();
+
 	bool TranslateFCGInames(char * sock, char * sock_user, char * sock_group);
 	bool InitFCGIChmodChownSocket(char * sock, char * sock_user, char * sock_group);
 	bool DropPrivileges(char * user, char * group);