Rather than requiring a traditional crontab install, the app now
leverages quantum-core (link below) to schedule the instance update/sync
task every 5 minutes. Some updates as a result:

  - The new job is scheduled at runtime in server.ex.
  - The update.exs script was refactored to be compiled along with the
    rest of the app as instances.ex.
  - Scheduler and Server modules were added for creating and executing
    the new update task
  - All shell scripts were removed, as they are no longer needed

https://github.com/quantum-elixir/quantum-core

This adds a couple of new scripts: install-crontab.sh and update.sh. The
install-crontab script does exactly that -- it installs a new crontab
that runs the update script every 5 minutes. An update script was added
to simplify the crontab a bit and to ensure the Elixir update script is
executed from the correct directory.