[LEDE-DEV] [wiki] Creation of discussion pages simplified

[Thomas Endt]

To make it easier to create discussion pages and post comments on wiki
pages, I implemented a namespace template for the talk: namespace.

To create a new discussion regarding a wiki page
  * just click on "discussion"
  * then "create this page"
  * then save it without any edits.

A nice discussion editor will appear only after saving (it will not be
visible in the preview).

Thomas