Viewport headers can't contain vimwiki links

[sidequestboy]

The following breaks the viewport functionality:

= [[other-wiki-page]] | project:other-project =

and the list is not auto populated for example until the link is changed to plain text

[nkakouros]

The same issue exists with markdown links:

# [other-wiki-page](other-wiki-page) | project:other-project

[nkakouros]

I created #271 that addresses this.