combine page and user post permissions

We had two conflicting may_create_post? and almost conflicting may_update_post? functions. They lived in the me and the page permissions.

We often have to load both to render the menus and all actions properly. Instead of having the two fight we now have posts_permission. It's only required in a few controllers.
Updating message as to why translation-related tasks might not run.
render nothing if wiki.body_html is nil

This used to raise an error because nil.html_safe is not defined.
Merge pull request #118 from azul/bugfix/render-group-home-with-empty-wiki

render nothing if wiki.body_html is nil
Merge pull request #117 from azul/bugfix/6665-bring-back-comments

combine page and user post permissions