1.6 - Add preview status for Node, Block, Menu, and Link

This is a work in progress.
- It adds a new class `Croogo.Lib/CroogoStatus`
- The `PublishableBehavior` class provide the functionality for the model layer
- A new method is added `CroogoHelper::statuses()`
- `Node.status`, `Block.status`, `Menu.status`, and `Link.status` is now a tristate value:

```php
    0 - Unpublished
    1 - Published
    2 - Preview
```
- `CroogoStatus::status()`: Obtain `status` for use queries. It uses `AuthComponent::user()`, checks with Acl.
- Add two new fields: `publish_start` and `publish_end`, useful to limit publish date range.  Conditions is injected during via `beforeFind()`

__Todo__

- [x] Tests

~~Having the behavior directly attached causing problems with existing tests.  Any suggestion on how to really split these out?~~

~~Oh, last commit (menu toggling) would actually be split over a separate PR). Please ignore that part.~~