Add basic caddy swarm role

Added caddy as swarm container. Uses templated Caddyfile which can be
set up for testing purposes for now.
Depends on docker and docker-swarm, and will keep its stuff where
docker-swarm sets itself up.

roles/caddy/templates/Caddyfile.j2

@@ -0,0 +1,26 @@
+{
+{%- if caddy_email is not none %}   
+    email {{ caddy_email }}
+{% endif %}
+
+{% if caddy_tls_use_staging is sameas true %}
+    acme_ca https://acme-staging-v02.api.letsencrypt.org/directory
+{% endif %}
+
+{% if caddy_use_debug is sameas true %}
+    debug
+{% endif %}
+
+{% if caddy_use_https is sameas false %}
+    auto_https off
+{% endif %}
+}
+
+{% if caddy_create_test_file_server is sameas true %}
+:80 {
+    file_server {
+        browse
+    }
+}
+{% endif %}
+