Turn relative links into absolute ones

Fix: Relative links (#419)

* Fix: Relative URLs in links

Feed discovery with relative URLs in links
Example: https://k47.cz/
Solution to the problem: #417

* Update Feed.php (Fix relative URLs in links)

We will replace the links (add the host if it doesn’t exist) in the content as well

* Update Node.php (Fix relative URLs in links)

* Update Reader.php (Fix relative URLs in links)

Remember the URL for further processing

* Update Link.php (Fix relative URLs in links)

* Update XmlParser.php (Fix relative URLs in links)

* Update Explorer.php

* Update Node.php

Delete tabs