Crawling unknown page should raise a log warning

[bastien-roucaries]

You should get something on stderr if something try to load non existant page. It will defect simple network scanner and raise some warning using log analyser. Use an exception Error404 or so on to do this (see next bug report for why)

At least here https://github.com/SimulPiscator/AirSane/blob/335e832047d718fd119f19b8078904ac93eba08b/server/mainpage.cpp#L69

[SimulPiscator]

I added some code to do this.