Support tomcat users

@bmuschko As we discussed in #107, supporting configure basic authentication user

closes #107
Currently, the DSL as proposed doesn't allow for multiple users and different roles. We should probably change this to the following:

    users {
        roles {
            role {
                rolename = 'tomcat'
            }
       
            role {
                rolename = 'role1'
            }
        }
     
        user {
            username = 'user1'
            password = '123456'
            roles = ['tomcat', 'role1']
        }
    
        user {
            username = 'user2'
            password = 'abcde'
            roles = ['tomcat']
        }
    }