Make use of the new advanced link handling in core

[iamdarkle]

With the new version of Flarum (1.4.0) I think there is a great potential to add different options to the extension related to the new extender that allow the user to add different behaviours like dofollow on internal links... etc.

Personally I'm not really into this, but seeing the huge interest in this from the community, in multiple Discuss threads... I think it would be great that before related extensions come out, this could be included from here.

Some interesting links on the subject:

• feature: adds advanced link handling in core flarum/framework#3455
• https://github.com/luceos/flarum-ext-dofollow