finalized and integrated buffer scan with fallback to temp file scan if other than clamav or proc_open not allowed/available

fixed validation of mimetype due to a possibly given charset, especialy because the detection itself returns it ^^

fixed fill questions fallback for rnd passes so allready used questions are avoided to be chosen again

fixed mantis 0015868: Anzeige von importierten Zuordnungsfragen (Rest vom ILIAS ist defekt Sammelreport ist noch offen)

[FIX]: 0019985: Creating local roles: cannot copy roles

fixed fix for second context and removed tmp workaround - found another not affecting issue, that might become a problem by any change in the calling/requesting/redirecting strategy