Seed URLs are rejected

I set the following seed:

`seed/seeds.csv`:
```
uri,type
http://a.b.c.d:8000/,html
```
(`a.b.c.d` is an IP address)

I get this in logs:
```
frontier | [main] INFO [o.d.s.c.SeedConfiguration] -
frontier | [main] WARN [o.d.s.f.i.FrontierImpl ] -
```

Start with the seed/seeds.csv reproduction and trace how SeedConfiguration passes the URL into FrontierImpl.addNewUri. Inspect the URI scheme and host validation that produces the logged rejection for an IP address. Done means the HTTP seed using an IP address is accepted without the unsupported-scheme warning.

Written by the indexing model from the issue text.