Add a JBoss SSO Login module.

Add a JBOSS SSO Login module that uses REST to connect to a configurable server url.
Configuration happens in standalone.xml and should look something like this:
```xml
<security-domain name="zanata.jbosssso">
     <authentication>
           <login-module code="org.zanata.security.JBossSSOLoginModule" flag="required">
                 <module-option name="serverURL" value="-- server url --"/>
           </login-module>
     </authentication>
</security-domain>
```
ObjectMapper seems to be (mostly) threadsafe.  Do you think it would be worth holding on to it for future logins?