Added getSections() method.

I found that is impossible to get template sections from a View object
so I made it possible. This is good expecially when AJAX comes into
play.
Added renderSections() method.

I found that is impossible to get template sections from a View object
so I made it possible. This is good expecially when AJAX comes into
play.

Since the property 'section' is updated once the View has been rendered,
the correct usage is that:
```php
$view = View::make('pages');
$sections = $view->renderSections();
```
Removed old property.
Removed old code.
Restored comment on render().
Include called class name in ModelNotFoundException
Cleaning.
Use proper instance of Relation

Bugfix from @anlutro's recent PR #2734
Merge pull request #2771 from adamgoose/master

Use proper instance of Relation
Fixed typo
Merge pull request #2773 from billmn/master

Fixed typo
Remove strtolower(), already done in snake_case()
Merge pull request #2782 from PhiloNL/fix/strtolower-snake-case

Remove strtolower(), already done in snake_case()
Blade blade.compiler separate from engine.
Add mergeCollection, diffCollection and intersectCollection functions with tests
fixed typo
Fix missing variable.
Merge pull request #2787 from sergeizelenyi/patch-1

fixed typo
Implement diff and intersect on Support\Collection
Rename merge, diff and intersect functions to match those on Support\Collection