Stabilize when running without MQTT

[pzbitskiy]

• Original version drained "free heap" as shown on the /status page from 43% to 22% in one hour that lead hanging on /control page load. Sometimes it triggered reboot.
• New code does not have such issue, "free heap" shows 42-39% all the time and /control page continues to work.

This is possible related to #1

[pzbitskiy]

I'm not sure what exactly helped with memory consumption.
I checked both mqtt client fork and esp8266 String implementation, and cannot spot an issue - empty string assignment calls assignment operator that copies into internal buffer, and it gets destructed later anyway.
I also checked ArduinoJson, using a global static StaticJsonDocument looks OK even they do not recommend global JsonDocument and using String types because of copying. I'm not sure how do they track and destroy all String values (like from this assignments rootInfo["mode"] = hpGetMode(currentSettings)) but looks working fine - having memory usage stable.

[pzbitskiy]

An update: uptime is 9d w/o MQTT with 40-42% free heap. Couple days ago LED become ON. Today I added HA + MQTT, no memory issues for few hours.

[dzungpv]

Thanks