Make plugin hooks send out more information

Add this point you only get information that "something" happend on the given
hook. By adding more information to the hook, plugin creators can do more
interesting stuff.

* The first params remains the $APP name (to maintain backwards compatability)
* The second params sends in the action that happend, for domain this can be:
  "add", "clear" or "remove"
* The third param sends in the argument that was passed to the original
  function, for domain that would be a list of all the domains that was given.

One reason this addition would be great for plugin owners, is that when you have
a web tool over Dokku, and someone creates a domain over the CLI, we a plugin
can send back information about the event to the webapp over an API. That way
the webapp is always up-to-date with the Dokku installation.

Signed-off-by: Jeroen van Baarsen <jeroenvanbaarsen@gmail.com>

plugins/domains/commands

@@ -75,7 +75,7 @@ case "$1" in
     for DOMAIN in "$@"; do
       echo "$DOMAIN" >> "$DOKKU_ROOT/$APP/VHOST"
     done
-    plugn trigger post-domains-update $APP
+    plugn trigger post-domains-update $APP "add" "$@"
     for DOMAIN in "$@"; do
       dokku_log_info1 "Added $DOMAIN to $APP"
     done
@@ -89,7 +89,7 @@ case "$1" in
 
     rm -f "$DOKKU_ROOT/$APP/VHOST"
     dokku domains:setup $APP
-    plugn trigger post-domains-update $APP
+    plugn trigger post-domains-update $APP "clear"
     dokku_log_info1 "Cleared domains in $APP"
 
     ;;
@@ -110,7 +110,7 @@ case "$1" in
     for DOMAIN in "$@"; do
       sed -i "/^$DOMAIN$/d" "$DOKKU_ROOT/$APP/VHOST"
     done
-    plugn trigger post-domains-update $APP
+    plugn trigger post-domains-update $APP "remove" "$@"
     for DOMAIN in "$@"; do
       dokku_log_info1 "Removed $DOMAIN from $APP"
     done