Bring Liquibase to play-cms

Bring liquibase to the demo project. The following settings are required enable usage of liquibase

# use persistence unit with disabled schema generation
jpa.default = "liquibasePersistenceUnit"

liquibase {
  # copy settings from db section
  driver = ${db.default.driver}
  url = ${db.default.url}
  user = ${db.default.username}
  password = ${db.default.password}

   # choose enter point for liquibase changelogs
  changelog = "classpath:liquibase/master.xml"
  # turn liquibase on/off
  enable = true
}

conf/liquibase/master.xml contains following include <include file="liquibase/play-cms-master.xml"/> . This is the enter point of the liquibase in play-cms project. This line is essential since we have only project specific changesets here.