Icon party!

• FIXED: invisible app icon and default window icon in Linux
• ADDED: .deb package for Linux builds
• FIXED: size column was sorting by date, not size
• FIXED: could not exit from dock or by sending SIGINT to react-explorer process
• IMPROVED: pathbar now accepts fake ~ that will resolve to user home (even in Windows!)
• FIXED: pathbar outline still appeared below toolbar buttons