SSH connection status indicators

- Add Connected bool field to vfs.Entry and RemoteMount
- Track connection status in sshState.connectedHosts
- Show status icon (connected/disconnected) in pane header when browsing remote host
- Async SSH connection test with cancel support for Add Host dialog
- Colored labels and styled help text in SSH dialogs
- Confirmation dialog when deleting manually-added SSH hosts

vendor/golang.org/x/sys/windows/aliases.go

@@ -8,5 +8,6 @@ package windows
 
 import "syscall"
 
+type Signal = syscall.Signal
 type Errno = syscall.Errno
 type SysProcAttr = syscall.SysProcAttr