Store language selection for each channel

The availability of multiple audio streams and separate languages in left and right audio channel varies between channels. Such preferences should be stored separately for each channel and be restored each time the channel is used.

Note that there are channels which don't send multi-language at all times. Me-tv should if possible fall back to single-language operation if this can be detected, but keep the previous configuration setting so that it can switch back when the channel moves back to multi-language transmission.