Fixed connection issue in mail account import tool.

Added remote functions config_value_get, config_value_add, config_value_update, config_value_replace and config_value_delete to access the sys_config key / value store in ISPConfig from remote api.

Update ispconfig.css to fix #select_server a that is affected by #sidebar a padding of 10px. Already pr'ed and merged in master via !766. Perhaps can be merged with stable too?

Add description text for logging options.

global option to enable pagespeed with nginx - allows to enable pagespeed even if no webserver-config is selected

Reseller is able to see a list of all clients and not just of his own clients in select field in the head of domain list when domain module is active.

See issue #4984

. Thank's to Oliver for the fix.