First batch of staypuft models

    First batch of staypuft models
    
    This includes the new custom models for staypuft and the join models
    for the has_many :through relations. Not yet included are the
    join models which connect to native foreman types (HostGroup, etc.)
    or any extensions to foreman models -- that will be a later commit.
    
    Also, the scaffolding for tests is included for now, but it will
    be removed when we add the model rspec tests.