Allow normal users to view message wall greetings

Previously, it was impossible to view another user's Message Wall
Greeting unless you had the 'walledit' permission - this is obviously
not in the spirit of a wiki, as all pages should at least be viewable by
everyone. This change lets you do everything but edit another user's MWG
without 'walledit' :)
Merge pull request #4040 from WikiaVolDev/VOLDEV-73

VOLDEV-73: Allow normal users to view message wall greetings