Correcting EmpireAvenue module to work with Agorava core 0.6.0

OAuth 2.0 final support in Agorava Core allows EmpireAvenue to work normaly

Added a maven module to initiate OAuth flow and retrieve an acces token

It can be laucnch in the IDE or in command line with :

`mvn clean install -Pauthenticate -DskipTests`