Figure out if we want/need network connectivity checks

Checking if the network is up is not as straight forward as one might think, it has a lot of false positives depending on the technique. We should research the best (multiplatform) ways of doing this and whether we really need it.

I've tested the client as it is right now, and how it behaves with network connectivity loss, and it seems to do just fine, but we might want to inform the user about potential network loss.

(from redmine: created on 2013-05-20, closed on 2013-09-20, duplicates #1337 (closed), duplicates #6059 (closed))