improve(model-editing): add validations and editing for Model and Diagrams


- [x] Model
  - [x] `title`
    - required and minlength of 2
  - [x] `version`
    - required and test against [Semver](http://semver.org/) RegExp pattern
  - [x] `authors`
    - required and minlength of 2

![image](https://cloud.githubusercontent.com/assets/1885333/5483846/8df336f8-8651-11e4-97c3-0f777b940f75.png)

- [ ] Diagrams
  - [ ] `name`