Keep 0conf channels live if funding gets reorg'd out

[TheBlueMatt]

When a channel's funding gets reorg'd out (after its locked in) we currently just FC the channel since we don't have logic to re-sign channel announcements with the new SCID or swap the old SCID for the new one at all. We should fix that, though, given the prevalence of 0conf channels, since this now implies we will get some FCs any time we open a channel that gets confirmed in a block which is eventually reorg'd.