Feature/cleanup wp links

Aims to replace links pointing to issues/planning elements controller wherever possible. This is for now limited to singular actions (new, create, update, edit, show, not delete). 

* The links on the index list where removed
* Quickinfo links (e.g. \#18\ inside a wiki page) now point to work_package#show. This is also true for quickinfo links.
* Activities now do look the same for issues and planning elements. I tried to mark update vs create actions. But this conflicts with the search page, so I removed this functionality.

OP Issue: https://www.openproject.org/issues/1418