Namespace build configurations of modules, make more things into constexpr
(not fully finished though)

Unify code using ...Count() to parse IDs

Avoid using unsigned char aka uint8_t as index, prefer size_t
as most code already uses it anyway. Making sure we never accidentally
truncate the value or try to read it as 32bit-wide. Also, simplify
access to built in containers, since those use the wide type as well.

Renames led and button types, more consistent initialization and field access.

- general conversion from .ino modules into a separate .cpp files
- clean-up internal headers, place libraries into .h. guard .cpp with _SUPPORT flags 
- fix some instances of shared variables instead of public methods
- tweak build system to still build a single source file via os environment variable ESPURNA_BUILD_SINGLE_SOURCE

* 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)

- use similar to relay & wifi, configuration through helper methods that
  use indexed defines
- clock cycles for led delay polling
- button mode defaults