Removed redundant `meta[robots=noindex,nofollow]` in administration.
PhpDoc edited in `cs\Config` in order to improve external usage of protected property.
Removed remaining stuff from `cs\Page::get_debug_info()`
Removed theme-specific things from `cs\Page`, functionality moved to theme itself:
* `System/Page/get_header_info` trigger
* `cs\Page::$header_info` property
* `cs\Page::$user_avatar_image` property
* some other corresponding stuff removed

`core['show_footer_info']` and `core['footer_text']` system parameters removed as redundant.