sensors: move voting into sensors module

- voting is now at a central place instead of duplicated within the
  estimators
  -> this also means that estimators that did not do voting so far,
     now have voting, like ekf2
- estimators requiring more than that can still subscribe to the raw
  sensors
- allows sensors_combined to be 3 times smaller
  - reduces logger, memcpy (cache) & RAM overhead
- all modules requiring only 1 or 2 sensor values now automatically get
  the voted result
- this also adds voting to baro