Get rid of hard coded IPs (#441)

Replace them with:
* containers' hostnames
* gateway's IP address for default SMTP_HOST
* Core: when SMTP_HOST undef, echo the default value
* docker-compose: add port mapping
* docker-compose: drop network driver conf
* Exim macro: use localhost as LMTP host
* Update README.md
* docker-compose: Limit port mapping to loopback
* Update other docker-compose example files

docker-compose-postorius.yaml

@@ -16,9 +16,11 @@ services:
     - DATABASE_URL=postgres://mailman:mailmanpass@database/mailmandb
     - DATABASE_TYPE=postgres
     - DATABASE_CLASS=mailman.database.postgresql.PostgreSQLDatabase
+    ports:
+    - "127.0.0.1:8001:8001" # API
+    - "127.0.0.1:8024:8024" # LMTP - incoming emails
     networks:
       mailman:
-        ipv4_address: 172.19.199.2
 
   mailman-web:
     image: maxking/postorius:0.3
@@ -36,9 +38,11 @@ services:
     - DATABASE_URL=postgres://mailman:mailmanpass@database/mailmandb
     - SECRET_KEY=ksjdbaksdba
     - UWSGI_STATIC_MAP=/static=/opt/mailman-web-data/static 
+    ports:
+    - "127.0.0.1:8000:8000" # HTTP
+    - "127.0.0.1:8080:8080" # uwsgi
     networks:
       mailman:
-        ipv4_address: 172.19.199.3
 
   database:
     environment:
@@ -51,13 +55,6 @@ services:
     - /opt/mailman/database:/var/lib/postgresql/data
     networks:
       mailman:
-        ipv4_address: 172.19.199.4
 
 networks:
    mailman:
-     driver: bridge
-     ipam:
-       driver: default
-       config:
-       -
-         subnet: 172.19.199.0/24