add attachments from server storage

You can now add files from the server storage with elFinder

Save attachments directly to storage

• There is now a special connector.roundcube.php file, so that you can use this, instead of connector.minimal.php
• Configuration of basepath is now done in config.inc.php
• It's now possible to save E-Mail Attachments in the configured storage. For this, there is a new config parameter in config.inc.php to specify the right path. If this path doesn't exist, it will be created automatically.

Better authentication

• I have changed the authentication mechanism. The Roundcube session is now directly used.
• Added skin support for classic skin