[pvr] uses ChannelNumberLabel instead of ChannelNumber at all missing places

This is a follow-up of #5290 where we missed some adjustments to Confluence and the GUIInfoManager.

First this adds the properties `SubChannelNumber` and `ChannelNumberLabel` to the Video- and MusicPlayer. And second this replaces all places where we use `ChannelNumber` with the new property `ChannelNumberLabel`.

@opdenkamp please take a look as this is more a fix than an enhancement and we should merge this before the 15 Sep. (Alpha4)