Use express' error handling mechanisms

Rather than throwing errors, pass then to express' 'next' parameter,
which correctly handles them and then displays an appropriate error page
for the environment.
Don't use winston's handleExceptions option

When this option is enabled, stack traces end up being compressed onto a
single line, which makes it very difficult to figure out what the actual
error was. This doesn't affect the actual process, which will still exit
after an uncaught exception, as it did with this option enabled.
Add logging to the popit-daemon-debian init script

This will hopefully give a bit more of an insight into why the process
sometimes restarts. The solution was adapted from this SO answer [1].

If this solution works then it would be good to make all logs go to
stdout/stderr rather than try to write then to a file, then add
the file we write to into logrotate.

[1] http://stackoverflow.com/a/12662904