Allow users to post on a forum if they have only edit rights on that forum

Consider the following set up:

• Admin installs the forums application and restricts edit rights to admins
• Admin then creates several "forum" pages and gives edit rights to some group each, e.g in "Forums.Forum1" the group "XWiki.ForumGroup1" gets edit rights.

expected behavior

• users in the "XWiki.ForumGroup1" group see a "add topic" button in "Forums.Forums1" (only)

actual behavior:

• user in that group do not see that "add topic" button in any forum, including "Forums.Forums1"

This is just an UI issue, as these users are able to create pages, and thus forum topics manually.