[keycloak-dev] Keycloak server config

[Stian Thorgersen]

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