Bugfix on db-Class (datalog Update)

FS#2288 - Importer for data from Plesk control panel (first INCOMPLETE version, see bugtracker for status)

- Improved datalog functions.

Extended datalogUpdate and datalogInsert function in mysql library so that insert_data and update_data arguments can be passed as array too.

Also removed the calls to the db closeConn calls in favor of
destryong the connections on the class __destruct() 's..

Since firebird db had a closeConn as well, changed its __destruct
to calls its own personal closeConn which otherwise left unmodified.

Refs: 1722

Added destructor and session write to app class instead.

http://bugtracker.ispconfig.org/index.php?do=details&task_id=1671

- fix indentation
- get it nearer than similar server/lib/ files

Fixed general utf8 encoding problems when data is passed from frontend to server, this fixes also bug FS#1065 - Special characters in autoresponder subject may break the autoresponder 

Fixed: FS#1012 - Delete all records (domains, ftp users, etc.) of a client when the client gets deleted.

Changed: removed datalog update function in tform.inc.php and just left the stub function there for legacy support with a call to the new function in the db_mysql.inc.php.

- updated the debian installation instructions

- Updated Debian installation instructions.

- Add some functionallity to MySQL class

- Fixed several bugs.

Several fixes to avoid strict warnings. Made a variable public in db_mysql.inc.php. Added missing language tokens to en_users.lng