Generalization for databse classes

[Del-S]

BeaconEntry, WirelessEntry, CellularEntry and SensorEntry can have parent class with these variables:

• int id
• int fingerprintId
• long timestamp
• long scanTime
• long scanDifference

[Del-S]

After this FingeprintScanner functions can be reworked into one:

• calculateBeaconScanDifference()
• calculateWirelessScanDifference()
• calculateCellularScanDifference()
• calculateSensorScanDifference()

Reword into single one calculateScanDifference().