Experimental quvi 0.9 support

This isn't quite complete, but it works. The biggest things we need to
work on are A: disabling the quvirc, and B: prettifying the output of
ytsm-cronjob. The former looks like it will be difficult or hackish, the
latter is probably solved with trivial I/O redirection.
Partial prettification of cronjob, disable quvirc

So it turns out that man quvi, one of the shortest man pages I have ever
seen, spends a couple lines on QUVI_CONFIG. Not sure how I missed that.
Both of the issues mentioned in the previous commit message have been
fixed. QUVI_CONFIG now points to /dev/null, which produces a warning on
stderr. That isn't a problem because we redirect quvi's stderr to
/dev/null anyway for the sake of formatting.
Merge branch 'master' into quvi-0.9
Revert "Merge branch 'master' into quvi-0.9"

This reverts commit d88c8a8ca9bed77ff7885d04ad1c274863ec85f4, reversing
changes made to 6c444a6458d0656394ce370257395a2665de8a49.

I suspect that I partially broke ytsm-cronjob in the recent cleanup.
Reverted until I can figure out what went wrong.
Experimental change from quvi to youtube-dl

ytsm-cronjob might be better off moving to yt-dl than to quvi 0.9. The
only issue I see is that yt-dl doesn't seem to have a mechanism to
bypass the user's youtube-dl.conf. It might be possible to do something
like 'HOME="$some_other_dir" youtube-dl http...', but I will have to
investigate this further.
Disabled youtube-dl.conf with HOME=$ytsm_dir.

The solution proposed in the previous commit worked exactly as I hoped.
We now set $HOME to $XDG_CONFIG_HOME/ytsm to disable a user's main
youtube-dl.conf. There isn't much we can do about a
/etc/youtube-dl.conf, unfortunately.
Updated README for youtube-dl.
Merge branch 'youtube-dl'

This change switches the backend from quvi 0.4 to youtube-dl. yt-dl has
proven to be much easier to work with than quvi, particularly in
comparison to quvi 0.9, which makes everything about ten times more
complicated than it needs to be for no obvious reason.