Introduced WifiManager_ssid variable and documented user_config.h (#289)

* Commented user_config.h to clarify usage of WifiManager

* Introduced WifiManager_ssid variable

* Added changes to Test_config.h too

OpenMQTTGateway.ino

@@ -489,7 +489,7 @@ void setup_wifimanager(){
     //fetches ssid and pass and tries to connect
     //if it does not connect it starts an access point with the specified name
     //and goes into a blocking loop awaiting configuration
-    if (!wifiManager.autoConnect(Gateway_Name, WifiManager_password)) {
+    if (!wifiManager.autoConnect(WifiManager_ssid, WifiManager_password)) {
       trc("failed to connect and hit timeout");
       delay(3000);
       //reset and try again, or maybe put it to deep sleep