* Sensors: refactor configuration

- move sensor implementaion to the .ino,
  remove dependency undef / define from sensor files
- update test/build/sensor.h from SENSOR_SUPPORT
- allow to change sensor config variables externally
- `#include <...>` for global headers and libraries,
  fix relative path for math library

* add missing sns <-> i2c dependency

* ledrelay should return relay_none as default

* rollback to original test header

* include debug header when requested (relative)

* 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).