add travis build status on Readme.md

add travis CICD

fix platform and platform packages deps

update sensor reading routine

lock lib dependencies

create CHANGELOG

manage OTA password and port via config.json file

remove Secrets.h

safely merge user configuration from config.json with defaults

add config.json boilerplate

update README.md - config.json usage

add config.json boilerplate

manage also ssid and network password + mqtt user credentials with config.json

Access-point portal even for other configurations (MQTT, AP mode, etc)

coding style