Remove listener limit on supervisor's log stream

Each worker adds 6 listeners to the supervisor's LogWriter when their
logs are fed through the supervisor's stdout. When the maximum number
of listeners (default 10) is exceeded warnings are printed to the
console.
Support SIGHUP cluster restarting when undetached.

strong-deploy doesn't run sl-run "detached", it runs it as a direct
child process, as will an upstart job. SIGHUP needs to be supported all
the time, not just in detached mode (which I with strong-supervisor)
didn't have, anyhow, and would like to remove.
Load environment from app's .env file, if present.