#111 Frontend doesn't associate unknown files

[Anonymous]

When trying to open an unassociated file type within 7-
Zip File Manager by pressing Enter key, it creates error
message saying that there is no associating application.
What it should do is to execute the command shown at
the bold menu entry inside the 'System' submenu in 7-
Zip File Manager, to make it consistent with Explorer's
behaviour. Similarly, executing '7-Zip' -> 'Open'
command should have the same effect.