Clam Anti-Virus integration

Integrated **ClamAV**, which scans the `files` folder and its subfolders for corrupt files.

When a scan is performed by ClamAV (cronjob), the `oae-antivirus` module will automatically detect changes in the log file. The log file is created by ClamAV and contains a list of all the (possible) corrupt files.

When a change is detected, we read the log file, fetch all the corrupt content items and rename the file. E.g.: **'Chapter 2'** will become **'[CORRUPT] Chapter 2'**. The location of the source file will also be different, since the file will be moved by ClamAV to a separate folder.