Added initial support for Oukitel Smart Switch. This is a 2 outlet plug
that has the same pinout as the YiDian XS-SSA05.

* Added the configuration for the second generation OBI devices.

* Added link to the OBI Wifi Schuko Plug V2 as well as included the device in the readme.

* Restored the default configuration accidentially changed by a previous commit.

* Renamed the OBI-V2 device to EUROMATE_WIFI_STECKER_SCHUKO_V2 as suggested by mcspr.

* Fixed spelling of comment to the proper wording Schuko.

* Works with many different ultrasonic sensor models: HC-SR04, SRF05,
  SRF06, DYP-ME007, JSN-SR04T & Parallax PING)))™.
* Built-in digital filter method ping_median() for easy error correction
  (use SONAR_ITERATIONS build flag to configure).
* Allows setting of a maximum distance where pings beyond that distance
  are read as no ping or clear (use SONAR_MAX_DISTANCE build flag).