webui: apply modules-... style globally

Otherwise, some things are still hidden
(or, depend on the order of incoming messages)

Make thermostat code use those as well, instead of injecting
thermostatVisible in every json payload

code/espurna/button.cpp

@@ -773,9 +773,7 @@ void _buttonRelayAction(size_t id, ButtonAction action) {
 namespace {
 
 void _buttonWebSocketOnVisible(JsonObject& root) {
-    if (buttonCount()) {
-        root["btnVisible"] = 1;
-    }
+    wsPayloadModule(root, "btn");
 }
 
 void _buttonWebSocketOnConnected(JsonObject& root) {