Add wrapper script for easier setup of the docker-mailserver (#280)

To setup the mailserver large snippets of shell code had to past in a
console. Instead of:

  mkdir -p config
  touch config/postfix-accounts.cf
  docker run --rm \
    -e MAIL_USER=user1@domain.tld \
    -e MAIL_PASS=mypassword \
    -ti tvial/docker-mailserver:latest \
    /bin/sh -c 'echo "$MAIL_USER|$(doveadm pw -s SHA512-CRYPT -u
  $MAIL_USER -p $MAIL_PASS)"' >> config/postfix-accounts.cf

you can specify:

  ./setup.sh email add user1@domain.tld mypassword

This wrapper script can be easily extended. It uses the scripts already
builtin.

setup.sh

@@ -0,0 +1,94 @@
+#! /bin/sh
+
+##
+# Wrapper for various setup scripts included in the docker-mailserver
+##
+
+if [ -z "$DOCKER_IMAGE" ]; then
+  DOCKER_IMAGE=tvial/docker-mailserver:latest
+fi
+
+_usage() {
+  echo "Usage: $0 <subcommand> <subcommand> [args]
+
+SUBCOMMANDS:
+
+  email:
+
+    $0 email add <email> <password>
+    $0 email del <email>
+    $0 email list (not yet implemented)
+
+  config:
+
+    $0 config dkim
+    $0 config ssl
+
+  debug:
+
+    $0 debug fetchmail (not yet implemented)
+"
+  exit 1
+}
+
+_docker() {
+  docker run --rm \
+  -v "$(pwd)/config":/tmp/docker-mailserver \
+  -ti $DOCKER_IMAGE $@
+}
+
+case $1 in
+
+  email)
+    shift
+    case $1 in
+
+      add)
+        shift
+        _docker addmailuser $@
+        ;;
+      del)
+        shift
+        _docker delmailuser $@
+        ;;
+
+#      list)
+#        ;;
+
+      *)
+        _usage
+        ;;
+    esac
+    ;;
+
+  config)
+    shift
+    case $1 in
+      dkim)
+        shift
+        _docker generate-dkim-config
+        ;;
+
+      ssl)
+        shift
+        _docker generate-ssl-certificate
+        ;;
+      *)
+        _usage
+        ;;
+    esac
+    ;;
+
+  debug)
+    shift
+    case $1 in
+      fetchmail)
+        _docker sh -c "cat /etc/fetchmailrc_general /tmp/docker-mailserver/fetchmail.cf > /etc/fetchmailrc; /etc/init.d/fetchmail debug-run"
+        ;;
+    esac
+    ;;
+
+  *)
+    _usage
+    ;;
+esac