Fixed Open Issue #3789 php-fpm reload workaround targeted at Ubuntu 14.04 breaks newer/fixed PHP packages on Ubuntu 14.04

- simply call nginx -t instead of /usr/sbin/nginx -t; works if nginx is not located in /usr/sbin, but elsewhere in the PATH.

- nginx: do a syntax check because on some distributions, the init script always returns 0 - even if the syntax is not ok (how stupid is that?)

- Added "actions" framework in server to replace the functions provided by the core modules
- Moved system update function from remoteactins core module to software update plugin.

- Fixed FS#1745.

- changed GRANTs for slave servers on multiserver setups
- added option for clients to change path of ftp users (inside webroot)
- extended software packaging system (return status of install)
- added 2 plugins for automatically create symlinks webmail and phpmyadmin on each website (not enabled by default)

- Improved installer and updater for multiserver mode. Modules and plugins were only configured if the selected service is available on the server.

Moved server modules and plugins to new directory and updated the installer to create the symlinks for the modules and plugins from *-available to *-enabled directory.
Fixed a typo in mailfilter template.

- improved several functions in site module
- added server classes to restart services