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.

site-dev.yml

@@ -0,0 +1,6 @@
+---
+
+- hosts: docker_swarm_manager_node
+  roles:
+    - whoami
+    - wallabag