Add models for cloud orchestration

This PR is split from original PR #333  (to be discarded). It focus only on the models for orchestrations. 
The master PR #523 covers the design and progress of the support for orchestration including AWS CloudFormation and OpenStack Heat.
![orchestration](https://cloud.githubusercontent.com/assets/7047579/4719534/6144c4e0-592a-11e4-9dc1-7d882f00f947.png)

No need for an after block here:

```ruby
  factory :orchestration_template_with_stacks, :parent => :orchestration_template do
    stacks { [FactoryGirl.create(:orchestration_stack)] }
  end
```