Training module: Use validator for more inputs

[blackcoder87]

Description

• Use validator for more inputs.
• Fix redirect on negative validation result.
• Fix has-error class being applied to all inputs.
• Require at least the address of the voice or gameserver if enabled.

PHP Fatal error:  Uncaught TypeError: Modules\Training\Models\Training::setShow(): Argument #1 ($show) must be of type bool, null given, called in application/modules/training/controllers/admin/Index.php on line 109 and defined in application/modules/training/models/Training.php:491
Stack trace:
#0 application/modules/training/controllers/admin/Index.php(109): Modules\Training\Models\Training->setShow()
#1 application/libraries/Ilch/Page.php(243): Modules\Training\Controllers\Admin\Index->treatAction()
#2 application/libraries/Ilch/Page.php(137): Ilch\Page->loadController()
#3 index.php(68): Ilch\Page->loadPage()
#4 {main}
  thrown in application/modules/training/models/Training.php on line 491

PHP Fatal error:  Uncaught TypeError: Modules\Training\Models\Training::setContact(): Argument #1 ($contact) must be of type int, string given, called in application/modules/training/controllers/admin/Index.php on line 101 and defined in application/modules/training/models/Training.php:307
Stack trace:
#0 application/modules/training/controllers/admin/Index.php(101): Modules\Training\Models\Training->setContact()
#1 application/libraries/Ilch/Page.php(243): Modules\Training\Controllers\Admin\Index->treatAction()
#2 application/libraries/Ilch/Page.php(137): Ilch\Page->loadController()
#3 index.php(68): Ilch\Page->loadPage()
#4 {main}
  thrown in application/modules/training/models/Training.php on line 307

Type of change

• Bug fix (non-breaking change which fixes an issue)

This PR has been tested in the following browsers:

• Chrome
• Firefox
• Opera
• Edge