thermostat: clean-up and build fixes (#2601)

- update library esp8266-oled-ssd1306 to the latest version
- fix thermostat build issues
- simplify and clarify thermostat control logic
- add logs to thermostat control logic

code/espurna/button.cpp

@@ -20,6 +20,7 @@ Copyright (C) 2019-2021 by Maxim Prokhorov <prokhorov dot max at outlook dot com
 #include "mqtt.h"
 #include "relay.h"
 #include "system.h"
+#include "thermostat.h"
 
 #if WEB_SUPPORT
 #include "ws.h"