Interface change

Renamed mv_design to db_design. No idea why I named it mv_design
DS18B20 class now takes a few more parameters in the contructor
Base 1wire class now exposes reading as a property
take_readings.py includes Python3 shebang and implements new sensors
interface

[ticket: X]
Forgot to add db_design :)
Refactoring

Populated class variables in DS18B20.
Also removed deprecated line of code.