reversing transformation of range_id leaks protected votes about cliqrplugin

[luniki]

Instead create a random salt at install time, write it to the global config and transform IDs like this: md5("$salt-$cid")

[luniki]

Add check whether the Cliqr plugin is active in the range_id

[luniki]

when transformRangeId returns with a valid Course ID, we are in trouble.

[luniki]

Courses with an activated Cliqr will always show their Cliqr questions to everyone. This is done by design choice. Therefore it is enough to check state of the Cliqr plugin in the course of a given $cid.