Request: Ability to add clients to known client list from Network page

@yubiuser I've seen you have also be reading on the other discussion, I'm wondering if we should now undo the non-adding of the incomplete or failed devices? It should now be fine to add them as mock-devices as FTL can now convert them into "real" devices once more ARP data arrives (at least if it arrives within one hour after the mock device was created, we can tweak this timeout).