Allow using network profiles as nested profile for each other

[Gfrni]

When connecting through multiple SSH tunnels, network profiles cannot be reused inside each other.
For example:
Database A_db is accessible through tunnel A.
Database B_db is accessible through tunnel B.
Tunnel B is accessible through tunnel A.

So, I should create two network profiles:

1. A_tunnel which is used to connect A_db
2. AB_tunnel which is used to connect B_db

The problem: While I have already defined tunnel A settings in A_tunnel profile, I should define it again in AB_tunnel.

As a solution, I suggest reusing network profiles in each other, as nested fields.

Alternatively, similar to this earlier feature request, listing system-wide SSH hosts in network profiles menu solves this problem, because in system SSH configuration file, a host can be reused as a tunnel in other hosts, like this:

Host A
	(A settings)
Host B
	(B settings only, ignoring A...)
	ProxyCommand ssh A nc %h %p

[arhayka]

Thank you for the idea!