Start checks against local sites list for allowed reverse proxy forwards

First workflow for allow reverse proxy with different site names
for ispconfig panel.

TODO: Allow only for sites known to the system itself instead
of all or none.

- Use it like $app->conf('yourpluginname', 'config-key', 'value')
- omit the value to read the config value, provide it to set the value

Fixed login as

Fixed/Implemented: replaced intval() by $app->functions->intval() in all interface functions due to big number problem in intval()

- Added translations to global search.

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 a function to the remote api to get all virtual machines of a client.

Added destructor and session write to app class instead.

- Fixed date handling functions in remoting library.

Added global functions library which conatins a mail functin that supports attachments and a array_merge function that merges arrays that conatain numeric keys and strings correctly.

Added a option to debug the language files (show strings that are not contained in the lang file surrounded by #....#)
Fixed: FS#1063 - Missing language variables in shell user options