Add new V3.0 version of PZEM004T, not tested. Default to factory default address 0xf8, configurable through pzemv30Addr 8-bit number
Add 'frequency' measurement & 'hz' unit
Add pz.address that configures address
Implemented energy reset

Right now we only support a single device. No way to test this properly (mostly, how exactly we need to connect this stuff), so left as not implemented.

* 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)

* travis: move build flags tests outside of hardware header

* mqtt: fix typo

* travis: use files instead of bundling test cases into script

* fixup! travis: use files instead of bundling test cases into script

* fix variable expansion, remove custom h at the end

* add ade7953 to sensors list

* custom.h path as variable

* shellcheck

* fix printf syntax, silent again

* fix bash 4.3 treating empty array as unset variable