External sftp client integration

[kohanis]

Is your feature request related to a problem? Please describe.
Kinda. Just used to winscp integration from kitty, and it uses sftp:// instead of scp://

Describe the solution you'd like
To add current-winscp-like integration for custom sftp client, like allowing user to specify path and calling [user path to program] sftp://[email protected]:22
Maybe even just custom calls with masks like %login%, %ip% and %port%

I can probably try to implement it myself if functionality fits into the vision