Increate favicon retrieval timeouts
I've noticed that many favicons are not shown. Increasing retrieval timeouts in the hope that this yields better results.
OF-1885: Guard against SSRF by inpecting favicon results
The Openfire servlet that is supposed to be used to retrieve favicons from remote servers could be used to obtain anything. To prevent unauthorized use, this commit adds a check that verifies if the returned data is an image. If that's not the case, the returned data is ignored.
