turn MessagePages with assets in DiscussionPages

We can't convert them to the new message system without loosing the asset.
force mode of uploaded profile banners to be 0644 (graphicsmagick seems to ignore umask)
FileUtils calls expect a string not a Media::Tempfile

output_file is not guaranteed to be a String. So let's call to_s on it. Also makes the asset test pass.
Merge pull request #72 from Crabgrass/bugfix/profile-banners

force mode of uploaded profile banners to be 0644
Merge pull request #77 from Crabgrass/bugfix/turn-message-pages-with-assets-into-discussions

turn MessagePages with assets in DiscussionPages
cleanup and refactor page list rendering to use partial
link_to_name takes the avatar_id - not the user one

We might want to add some caching here later because fetching the avatar_id kind of defeats the purpose of link_to_name
page.owner and page.updated_by can be nil.
Merge pull request #78 from Crabgrass/bugfix/4341-fix-avatars-in-page-list

Bugfix/4341 fix avatars in page list