Add wsgi.py and Dockerfile (#187)

* Add a sample wsgi.py

* Add a sample Dockerfile making use of wsgi.py

* Use 'puppetdb' as default location for PUPPETDB_HOST

puppetboard/default_settings.py

@@ -1,6 +1,6 @@
 import os
 
-PUPPETDB_HOST = 'localhost'
+PUPPETDB_HOST = 'puppetdb'
 PUPPETDB_PORT = 8080
 PUPPETDB_SSL_VERIFY = True
 PUPPETDB_KEY = None