Support seeding of Dialogs

/cc @gmcculloug 

Related BZ:
https://bugzilla.redhat.com/show_bug.cgi?id=1155806
Prefer

```ruby
DIALOG_DIR = Rails.root.join("product/dialogs")
SEED_FILE  = DIALOG_DIR.join("service_dialogs.yaml")
```

However, is there even a need for two separate constants?