welcome controller: sort tenant names (for sidebar)
welcome#index: view: more post metadata
post controller: sort tenants

We have to do this because we sort the tenants in welcome#index also.
We define a `tenants_sorted` helper to unify the tenant-sorting
behavior.
view: sidebar: fix closing HTML tag
view: sidebar: add link to the site root

We use `raw` to include the non-breaking space `&nbsp;`; if we don't use
it, the string gets quoted and the HTML does not get parsed as intended.
'rails g controller Tenants show'
simplify migrations setup

Also, we add the `tenant_id` column for posts.
make use of 'tenants' concept

The biggest change is that now you can click on the sidebar on any
tenant (company department), and get all posts from that department.
style changes

Fix some broken HTML tags along the way.
use haml
post: bugfix: create with tenant_id
allow admin to edit posts

The `correct_user` method only set the `@post` variable by finding from
the current user's posts. For site administrators trying to edit other
users' posts, this meant that @post was always nil. As a result, the
site admin was always redirected to `posts_url`.
posts#index: bugfix: sort posts in controller, not view

Previously, we sorted in the view. This was broken because the view only
rendered 30 posts at a time, and so the view only had access to 30.
Thus, when it did the sorting, it only sorted the 30 it was given, and
not the entire array of posts.