Added first version of auto-calibrated noise sensor.

- calibrate for low noise levels
- relies on proper scale of microphone for high levels, this is
  unreliable
Added missing file.
Changed some constants based on experiments
Replaced duplicate string with a constant.
Resolved conflict with sensor specific preferences for loudness and
auto-calibrated noise sensor
Merge pull request #21 from senseobservationsystems/feature-auto-calibrate-noise

Feature auto calibrate noise