MultiHop - Selecting an entry or exit server should hide the server in the opposite list

[gorkapernas]

Description:

When selecting an entry server with MultiHop, this server should be hidden in the list of exit servers. The same should occur when selecting an exit server, this server should be hidden in the list of entry servers.

This change should only be implemented in the general list of servers, it should not affect the list of favorite servers.

Note: See desktop app implementation for further details.