ported network_peers to database generator

[oronila]

#1801 Completed the port. This is my first ever pull request to a open source repo so feel free to let me know if there are issues.

Some things to note are that although most of the methods were portable some required larger chunks of code and particularly, CreateNetworkPeer was extremely long so I left the db/network_peers.go file with the updated call sites for the SQL code as a helper function.

[stgraber]

I did a few tweaks on this one but I'm out of time to get this into today's release so it will go onto next month's.

The PR was missing one pretty important change, the removal of the old functions.
Once I did that, things mostly behaved but it's missing a compatible implementation of the Create logic. Getting the basics done is pretty straightforward but getting the peering+linking logic to match the old logic, that's a bit harder and not something I want to rush in hours before a release.