loader: make default delay 10 minutes

We don't need this odd special case for "forever".
webview: don't try to scroll when the view height is bogus
loader: don't use network service discovery, too unstable

It is quite easy to have NSD not responding. There are numerous
different error messages that can be seen while the service becomes
unresponsive. Just give up on its use and defaults to a generic name for
the default ping URL.
README: fix a typo
loader: take rendering time in account to let the page scroll correctly

The webview will trigger a callback when rendering time is known. The
activity will communicate the result to the loader. The loader will wait
a bit more to account for this time. Coupling is not ideal, but we don't
want to use an handler just for that.