User authentication via LDAP plugin

A new plugin adding user authentication via LDAP has been released. Note, this is still beta, suggestions and fixes are welcome, please use to report them. You can install it using the plugin manager in the WebGUI.

The FTP service already works, for SSH and SMB/CIFS i was not able to test them because the used Zentyal installation seems not to contain the required objectClasses (e.g. shadowAccount) to work properly with these services.