Fixed #4444 Error in the template htm /usr/local/ispconfig/interface/web/client/templates/reseller_edit_limits.htm

Fixed #4443 Error in the template htm /usr/local/ispconfig/interface/web/client/templates/client_edit_limits.htm

Fixed #4440 Error in the template htm /usr/local/ispconfig/interface/web/client/templates/client_template_edit_limits.htm

Improved the code that generates the ssh keys for clients and shell users and reorganized it into a central function.

Disable SSL cert check in ISPConfig mail user import tool to allow connections to ISPConfig servers with self-signed SSL certificates.

Shows last ip that was used to login successfully with this useraccount.
Logins from admins using loginAs are ignored

Implementiert Issue #4357
Zeigt die IP-Adresse des letzten erfolgreichen Logins auf dem Dashboard an.
Verändert die gespeicherte IP-Adresse nicht, wenn man sich via "Einloggen als" angemeldet hat.

Needed Database-Changes:

ALTER TABLE `sys_user` ADD `last_login_ip` VARCHAR(50) NULL AFTER `lost_password_reqtime`;
ALTER TABLE `sys_user` ADD `last_login_at` BIGINT(20) NULL AFTER `last_login_ip`;

Tested/Working on Ubuntu 16.04 LTS

Update language_edit.htm: add col-sm-3 to label-tag so that the language key is on the left side instead of the right side with all other keys.