Refactor Review schema handling

* Refactor Review schema handling with easier API use
Prevent url slug matching & set review schema name

* Add API filter testimonials_widget_review_name_length
* Auto create Review schema name from post content - like excerpt
* Prevent `has_archive` and `rewrite_slug` matching existing slugs and same
Load scripts and stylesheets only as needed

* Add API filter testimonials_widget_styles
* CSS wp_register_style and wp_enqueue_style slug changed from 'testimonials-widget' to 'Testimonials_Widget'
* [Load scripts and stylesheets only on Testimonials Page](http://wordpress.org/support/topic/load-scripts-and-stylesheets-only-on-testimonials-page)