input validations in installer

The test suite was missing a global keyword to access the $INPUT class.

This allows to treat empty parameters as default

This new wrapper ensures types are correct and accessed parameters are
actually set (with custom default fallbacks).

The wrapper is available in the global $INPUT variable. It accesses
$_REQUEST by default. If POST or GET is required, the post and get
members can be used:

$INPUT->int('foo',false); // access $_REQUEST['foo'], default false
$INPUT->post->int('foo'); // access $_POST['foo'], default 0
$INPUT->get->int('foo'); // access $_GET['foo'], default 0

The codebase still needs to be updated to make use of this.

Additional commit for closed Pull Request #100

Fix for FS#2522 / Now all places of $lang['restored'] are covered with the restored-date information

Formating of czech subscription emails