allow different login methods for imap server

The brackets are moved in to this file.

So the config.php for owncloud has to look like this now:
```php
'user_backends' => 
  array (
    0 =>
    array (
      'class' => 'OC_User_IMAP',
      'arguments' => 
      array (
        0 => 'imap.gmail.com:993/imap/ssl',
      ),
    ),
 ),
```
I made this change because some imap server need a different login-pattern, like
```
loginid.myserver.org
```
where the loginid == $uid

For those cases the config-file needs to look like this:
```php
 'user_backends' => 
  array (
    0 =>
    array (
      'class' => 'OC_User_IMAP',
      'arguments' => 
      array (
        0 => '.myserver.org:993/imap/ssl',
      ),
    ),
 ),
```