[Feature request] Use & configure clamd

Currently, ClamTK always uses clamscan to scan files. It would be nice to have an option to use the clamd daemon (clamdscan command). It will have the following differences:

• limited configuration - scanning by daemon doesn't support so many configs on scan time, they have to be configured earlier in config files. Would be nice if ClamTK can maintain this config;
• no db loading on every scan - the clamd has already loaded signatures and can just start the scan;
• utility the multithreading - clamd supports multithreading, what clamscan doesn't. This should improve the scanning time a lot