Bugfix: $app->system->unlink function had wrong parameter name, no files were deleted ever

- Fixed missing templates and language entries
- Previous subdomain mode can be used concurrently
- Changed log path to a more convenient location

- Added missing sys_tpl table to ispconfig3.sql and moved the definition of the table to the upd_0035.sql file as new tables cant be added in existing update files.
- added new ssl_key field to web_domain table.
- cleaned up unused code from apache plugin.

- Added new web folder named private to web folder layout. The folder is intended to store data that shall not be visible in the web directory, it is owned by the user of the web.
- Changed ownership of web root directory to root user in all security modes to prevent symlink attacks.
- Apache log files are now owned by user root.
- Improved functions in system library.

This option can be enabled under System > Server config and is named "Web folder protection".

Merged revisions 3049-3051,3053-3054,3058,3070,3074-3077,3082,3086-3088,3091-3092,3094-3095 from stable branch.

- Fastcgi: delete .php-fcgi-starter directory if another PHP mode is used.

- Improved support for multiple PHP versions. Additional PHP versions have now their own form and database table.

- Fixed UTF-8 support in email function.

- Added SNI config field in sysetm > server config > web.

Implemented: FS#1113 - Force client to use only allowed IPs

- Added SEO redirects (both Apache & nginx) to redirect from non-www website to www website or vice versa.
- Introduced placeholder [scheme] for redirect paths for alias and subdomains; will be replaced with http or https, depending on what the visitor uses.