Group header include

Header parts:

PVR_ERROR GetChannelGroupsAmount(int& amount) override;
PVR_ERROR GetChannelGroups(bool radio, kodi::addon::PVRChannelGroupsResultSet& results) override;
PVR_ERROR GetChannelGroupMembers(const kodi::addon::PVRChannelGroup& group, kodi::addon::PVRChannelGroupMembersResultSet& results) override;