Bug FS#267 - mail filter not hidden for client 

Fixing the way some User Interface text was used. For the quota on a mailbox I added 'in MB' so that the user knows what units the quota is in.

Now a client can view e-mail filters created by admin, but the client can't edit them. The client can submit a change, but it isn't input in the database, nor is the client told that the changes aren't made.

http://bugtracker.ispconfig.org/index.php?do=details&task_id=267&string=&project=3&search_name=&type[0]=1&sev[0]=&pri[0]=&due[0]=&reported[0]=&cat[0]=&status[0]=open&percent[0]=&opened=&dev=&closed=&duedatefrom=&duedateto=&changedfrom=&changedto=&openedfrom=&openedto=&closedfrom=&closedto=

This is to try to fix the bug where if a filter is created by an admin, then the user with the e-mail account can't see the filter. 

http://bugtracker.ispconfig.org/index.php?do=details&task_id=267&string=&project=3&search_name=&type[0]=1&sev[0]=&pri[0]=&due[0]=&reported[0]=&cat[0]=&status[0]=open&percent[0]=&opened=&dev=&closed=&duedatefrom=&duedateto=&changedfrom=&changedto=&openedfrom=&openedto=&closedfrom=&closedto=

Added missing strings from english language files to german language files. TODO: Translate missing strings

- Updated Debian installation instructions.

- Better Autoresponder script
- Fixed error in language file.

- fixed bugs when websites and dns zones were deleted.

- Added dutch translation (many thanks to Hans!)

- Changed shell of website linux user to /bin/false

Fixed: Several php notices for undefined indexes.