Decouple WifiInterface from Parser

This removes the need for WifiInterfrace <+> command processing to be included in the link. so parser does not need to see the config settings for wifi.
If Wifi doesnt set the At command callback, parser will return <X> for a <+> command

DCCEXParser.cpp

@@ -17,13 +17,10 @@
  *  You should have received a copy of the GNU General Public License
  *  along with CommandStation.  If not, see <https://www.gnu.org/licenses/>.
  */
-#include "config.h"
-#include "defines.h"
 #include "StringFormatter.h"
 #include "DCCEXParser.h"
 #include "DCC.h"
 #include "DCCWaveform.h"
-#include "WifiInterface.h"
 #include "Turnouts.h"
 #include "Outputs.h"
 #include "Sensors.h"
@@ -157,10 +154,15 @@ int DCCEXParser::splitValues(int result[MAX_PARAMS], const byte *cmd)
 }
 
 FILTER_CALLBACK DCCEXParser::filterCallback = 0;
+AT_COMMAND_CALLBACK DCCEXParser::atCommandCallback = 0;
 void DCCEXParser::setFilter(FILTER_CALLBACK filter)
 {
     filterCallback = filter;
 }
+void DCCEXParser::setAtCommandCallback(AT_COMMAND_CALLBACK callback)
+{
+    atCommandCallback = callback;
+}
 
 // See documentation on DCC class for info on this section
 void DCCEXParser::parse(Print *stream, byte *com, bool blocking)
@@ -392,11 +394,14 @@ void DCCEXParser::parse(Print *stream, byte *com, bool blocking)
             DIAG(F("Setting loco %d F%d %S"), p[0], p[1], p[2] ? F("ON") : F("OFF"));
         DCC::setFn(p[0], p[1], p[2] == 1);
         return;
-#ifdef WIFI_ON
+
     case '+': // Complex Wifi interface command (not usual parse)
-        WifiInterface::ATCommand(com);
-        return;
-#endif
+        if (atCommandCallback) {
+          atCommandCallback(com);
+          return;
+        }
+        break;
+
     default: //anything else will diagnose and drop out to <X>
         DIAG(F("\nOpcode=%c params=%d\n"), opcode, params);
         for (int i = 0; i < params; i++)