Add staging and development environments

Differentiated between both.

Development environment takes place locally, most directly through the
use of a vagrant machine on the development machine.

Staging environment mimics the final production environment, but is
situated on another server and, most probably, points to a different
address. Otherwise, however, it translates much more closely (dns
entries etc) to the production setup.

Production is just that, the final deployment.

staging.yml

@@ -1,11 +0,0 @@
-stable:
-  hosts:
-    tau:
-
-docker_swarm_manager_node:
-  hosts:
-    tau:
-
-testing:
-  hosts:
-    tau: