Fix crash after 'Launch exec file in terminal' choice.
Handle launching shortcuts correctly.

We should retrieve file info of shortcut target and use it on launch
instead of using still file info of shortcut itself - applications
should not handle shortcuts in any case but use given target URIs.
[#3578780]Pressing 'Enter' should activate all selected files, not current one.

That behavior is the same as with file managers such as Dolphin, Nautilus, Xfe.
It is still consistent with double-click behavior though because double-click
will do selection before activation so still single file will be activated.
libfm-demo: open extra folders in new windows if more than one activated.