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/pluginmsg.h

@@ -144,6 +144,8 @@ namespace Winix
 // winix is initialized,
 // now you can initialize your plugin
 // session pointer is null
+// you have to set the result status to true (env.res) if your
+// plugin was initialized correctly, otherwise winix will not start
 #define WINIX_PLUGIN_INIT					30080	
 
 // winix is ready to remove a plugin