Links have rel="nofollow" #314

Describe the bug

Links added by the user on an article or a pinned page have a rel="nofollow" attribute.

Steps to reproduce (if necessary)

Add a link in an article, either with markdown or HTML.
If the link is HTML and the user explicitly specifies another value for the rel attribute, this value is overridden when rendering the page.

Expected behavior

I see two issues with this:

• This prevents Mastodon profile validation (which requires a rel="me")
• This may reduce the visibility of the blogs since search engines apparently respect this directive

From the MDN:

Indicates that the linked document is not endorsed by the author of this one, for example if it has no control over it, if it is a bad example or if there is commercial relationship between the two (sold link).

• https://developer.mozilla.org/en-US/docs/Web/HTML/Link_types

IMHO this:

• shouldn't be applied at all on internal links (links to href="#something" or to other pages of the blog)
• should be applied by default on external links if the user doesn't specify anything else via a custom HTML anchor.

Application configuration

• Single mode or Multi-user mode? single
• Database? sqlite
• Open registration? no
• Federation enabled? yes

Version or last commit: 037fc40