show free heap in UI

src/main.cpp

@@ -403,6 +403,7 @@ protected:
     toHex(base,buffer,bsize);
     status["salt"] = buffer;
     status["fwtype"]= firmwareType;
+    status["heap"]=(long)xPortGetFreeHeapSize();
     //nmea0183Converter->toJson(status);
     countNMEA2KIn.toJson(status);
     countNMEA2KOut.toJson(status);

web/index.html

@@ -55,6 +55,10 @@
       <span class="label">TCP client error</span>
       <span class="value" id="clientErr">---</span>
     </div> 
+    <div class="row">
+      <span class="label">Free heap</span>
+      <span class="value" id="heap">---</span>
+    </div>  
   </div>
   <button id="reset">Reset</button>
 </div>