Ports downloader

[schmurtzm]

A feature dedicated to MMP users to download free engines and assets from Onion Ports.

PortMaster download script or the recent Onion Theme downloader can be a good inspiration.

[XK9274]

If no-ones picked this up for release of 4.4, or at the latest between 4.4 and 4.5 i'll probably have a go at it.