Various changes

Each commit includes a changelog. I've been working on this code for days on my computer. None of the commits should be broken (the script should work normally no matter which commit do you pick) but I had to edit my commits several times. In particular, my original debugging functions were a nightmare to set up, and replacing them force me to amend all the following commits. My original intention was to unblock YouTube videos again, but so far, I haven't had any luck. Newish videos on YouTube (from the last two years?) currently can't be downloaded in a merged format. The only options are: - using an M3U8 manifest to download video and audio segments - casting a video-only stream - or casting an audio-only stream. The first option works out of the box for the Tears of Steel test video at [`lolitemaultes/m3u8-urls`](https://github.com/lolitemaultes/m3u8-urls) and for streams from RTVE (Spanish public TV), but when CATT selects a YouTube M3U8 manifest, it just shows the Cast icon over black background. I couldn't find any way to root my ChromeCast, or figure out debugging. I tried casting video only then adding audio tracks, but not only does the ChromeCast not add them, it stops responding to CATT commands other than `catt stop`. Subtitling code should probably go to `subs_info.py`, but right now moving more code around will take me several days and result in no extra functionality. Any help is welcome. EDIT: - The mandatory checks on my computer didn't check for `api.py`... but I just made a tiny change in order not to break the API. (If input `device_desc` to `StreamInfo()` was optional, the dict `settings` replacing it must be optional too). - Edited the message for one of the first commits because in order to say `Click` instead of @click (I'm sorry if I pinged them for no reason).