[keycloak-dev] Keycloak server config

We're starting to get quite a lot of things that can be configured globally for a Keycloak server, with more coming soon. This includes: * Model DB * Audit DB * LDAP servers (currently per-realm, but it would be better to create global config that can be selected in realm) * SMTP servers (currently per-realm, but it would be better to create global config that can be selected in realm) * Server Alias (proposed to list yesterday) * Theme config (default theme, fallback theme, theme dir) I propose that we make this configurable through a single json file. In the distribution it would be standalone/configuration/keycloak.json. Like standalone.xml it would support system property expansion. An initial idea of the structure of the file: https://gist.github.com/stianst/9931577