Add CardDav and CalDav servers (#80)

* Add CardDav and CalDav servers

This implements the servers, but not the clients (yet). The implementation is essentially a proxy to Radicale (as a container in `docker-compose.yml`), with certain security assurances.

If you're upgrading, basically you'll need to create a new `data-radicale` directory, and everything else should just work.

This will also release v2.3.0 with those enabled by default. Tested with Thunderbird and Apple Calendar + Contacts.

To disable these, simply add the new config details and comment out or don't add the new `radicale` service from `docker-compose.yml`.

Related to #56

docker-compose.dev.yml

@@ -14,6 +14,29 @@ services:
       memlock:
         soft: -1
         hard: -1
+    mem_limit: '256m'
+
+  # NOTE: If you don't want to use the CardDav/CalDav servers, you can comment/remove this service.
+  radicale:
+    image: tomsquest/docker-radicale:3.5.4.0
+    ports:
+      - 127.0.0.1:5232:5232
+    init: true
+    read_only: true
+    security_opt:
+      - no-new-privileges:true
+    cap_drop:
+      - ALL
+    cap_add:
+      - SETUID
+      - SETGID
+      - CHOWN
+      - KILL
+    restart: unless-stopped
+    volumes:
+      - ./data-radicale:/data
+      - ./radicale-config:/config:ro
+    mem_limit: '256m'
 
 volumes:
   pgdata: