example: Add LevelSensor using Ethernet

It was tested on Arduino mega256 with W5100 shield and FC-28 soil moisture analog sensor

Change-Id: Ibb78e12d024df8bcbe522e013734e40a3a623b16
Origin: https://github.com/TizenTeam/webthing-esp8266
Bug: WebThingsIO#23
Signed-off-by: Philippe Coval <p.coval@samsung.com>

Author: rzr