Delete downloaded files after install

[bdovaz]

Issue Checklist

• [x] I'm using the latest u3d version
• [x] I ran u3d --help
• [x] I read the README
• [x] I made sure that a similar issue doesn't exit

Issue Description

Is there a way for it to automatically delete the downloaded files after it has been successfully installed? Otherwise it will end up filling up hard drive.

Thank you.