A podmin can now disable a spam account from the interface.
allow admins to close user accounts from the backend
* thanks to @maxwell for the initial work on this

port admin pages to bootstrap
* improve user view on admin search page
* add 'close account' link to each user in the search results
* keep the same blue color for the admin menu

some refactoring of the routes and the admin code
* try to be more RESTful (possibly)
* use a 'UserSearch' model for search parameters and querying

add changelog entry
Merge pull request #5046 from Raven24/admin_backend

[ready] admin backend improvements
Home page, registration page and robots.txt personnalization
Add my aspects link in the header
Add indication about testaccount and framasphere on the home page