The generated web page now supports multiple cameras and is usable on
idevices.

Modify pledge/unveil calls so LWP::UserAgent will work.

Now that multiple cameras are supported, keep going when one can't be
reached for some reason.

There's plenty of storage; may as well keep images around longer.

Since all we care about is whether the video-generating process is
still running, we can remove the SIGCHLD handling that updates the
list of child processes in favor of directly checking them when
decideding whether to generate a video or not.

 * Pass along camera quality kludge flag to Snap.
 * Print an error when waitpid finds a child not in the list
 * More directly search for today's video

Make the previous change here more tidy.

Multiple cameras can now have snapshots taken and videos
generated. The cameras are hardcoded for now. Images and videos go
into a per-camera spool.