Number of decimal places option for each sensor

[jgrocha]

Let users define the precision of each sensor.

Add this to the metadata on Arduino's EEPROM.

[jgrocha]

Arduino metadata contains precison.

 typedef struct {
  int id;
  char location[20];
  time_t installdate;
  char sensortype[20];
  char quantity;
  int metric;
  int calibrated;
  int decimalplaces;
  double cal_a;
  double cal_b;
} Sensor;

We need also the bluetooth address and update local SQLite database.