Fixes: #2902 - Implements systemd (#3017)

* Closes #2902 - Migrate to systemd from supervisord
* Closes #2902 - Migrate to systemd from supervisord

* Update systemd unit and environment file
* Add gunicorn.conf
* Update documentation and CHANGELOG.  Moved parameters around on service file
* Update Gitignore

contrib/gunicorn.conf

@@ -0,0 +1,22 @@
+# Bind is the ip and port that the Netbox WSGI should bind to
+#
+bind='127.0.0.1:8001'
+
+# Workers is the number of workers that GUnicorn should spawn.
+# Workers should be: cores * 2 + 1.  So if you have 8 cores, it would be 17.
+#
+workers=3
+
+# Threads
+#     The number of threads for handling requests
+#
+threads=3
+
+# Timeout is the timeout between gunicorn receiving a request and returning a response (or failing with a 500 error)
+#
+timeout=120
+
+# ErrorLog
+#     ErrorLog is the logfile for the ErrorLog
+#
+errorlog='/opt/netbox/netbox.log'