* 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
* join the conditions of the inner ifs
* add a uniqueness constraint to the model
* differentiate between author is a local or a remote user
* simplify controller/mailer functions
