Components and Pages: Unpublish page

[AZholtkevych]

Add the ability of stop serving a page publicly. In order to do so, it's necessary to:

• Remove the page entry from the ETS table
• Unload the page module
• Recompile stylesheets
• Generate an unpublished event

It's better to create a public function Content.unpublish_page/1 similar to publish_page/1 to take care of the actions listed above.