#40 Allow using channel on Peertube in addition to playlist

With the release v0.6.2 we add the new Peertube playlist system Previously, we used channel in place of playlist, even if they are not exactly the same. However, channel are now not usable in Prismedia, which is a shame as it's a powerful way to organize video in Peertube. Indeed, you may create channel that define global thematic (like cooking, technical video, ...) and then create playlist **inside channel** to organize videos in the channel (like dessert playlist, meat food playlist, ...). At the moment we create all playlist in the default channel, we need to increase this feature. Time to reintroduce the channel in prismedia! We may add an option to specify a channel in addition to a playlist. **This would be a Peertube feature only** Features: - Like playlist, we need to check if a channel exist, offer to create it if not, create the channel, then use it for the playlist later. - If no channel are specified, use the default channel as usual. - It has to be done before the playlist part, as playlist need a channel to be created. - If a non existing channel is specified and createChannel is false, then stop the upload