[#33779] JLayout and Event cleanup of categories views

http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=33779&start=0

This gets the categories_default_items JLayout to actually output data

It also adds in a more standardized set of events and implements this into the JViewCategories class
See the global idea here:
https://github.com/joomla/joomla-cms/pull/3231/files#diff-052d2cd54df63a9e6c7e13a1185a4dfeR12

But, as @Fedik, stated I think is better to put variables in the form:
```php
@var variable_type $variable  variable description
```