Allow user search by username, refs #275

Search was done by full name only, now it can be done by both full name and
username.
Also fixed the tests broken by cbcc1b77 and 22793cd0.
Nest private messages under /my/messages

They are accessible to the current user only, don't really need to be nested
under /users as they were before. Looks cleaner the way they are now.
Remove the prefix /my from all routes that had it

They are now nested directly in the root path (e.g. /activity, /home)
Routes under /webconference were changed to /room to avoid confusion with
the routes under /webconf.