Denon: default zero dB level for relative volume control is wrong

[mkulesh]

For premium version only

Currently, the default zero dB level is taken from the maximum volume value that is wrong since many receivers allow to set the relative master volume greater than 0dB.

The actual zero dB level shall be taken from receiver information message, zone-dependent parameter group Zone -> Volume -> MaxVolumeList:

        // <MaxVolumeList>
        //   <Param>
        //     <Absolute>OFF</Absolute>
        //     <Relative>OFF</Relative>
        //     <Value>98.0</Value>
        //   </Param>
        //   ....
        //