Added new questions for create extensions and themes

### Improvement for pagekit console 

This PR just add 3 new questions:
- Description
- License (default MIT)
- Homepage

For **extension:generate** and **theme:generate** commands

![image](https://cloud.githubusercontent.com/assets/1450270/4486953/9c08f6c6-49f0-11e4-978f-1a3b2d5d4983.png)

Also add the description for `DefaultExtension.php` class

```php
 use Pagekit\Framework\Application;
 use Pagekit\Extension\Extension;
 
/**
 * %DESCRIPTION%
 */
 class %CLASSNAME% extends Extension
 {
     //--
 }
```

And for `DefaultTheme.php` class

```php
 use Pagekit\Framework\Application;
 use Pagekit\Theme\Theme;
 
/**
 * %DESCRIPTION%
 */
 class %CLASSNAME% extends Theme
 {
     //--
 }
```

PD: This is my first PR for a project... Please be comprensive... :smile: :+1: