Fix "now playing" update and add graceful closure

[andrewsayre]

This PR fixes a few issues:

• Removes player_id from the controller class and corrected methods that were still using the hard-coded player_id from device 0. This resolves the issue where the now playing media was not updating on devices other than the first one.
• Standardized usage of host and post so that it is used consistently throughout and removed host and post from connect as this was redundant to the parameters passed into init.
• Close is now a coroutine and contains logic to ensure a graceful shutdown.
• Added missing package pytz to requirements and setup.py

[easink]

Nice work