Fixes to asset manager to ensure there is no crash on DNS resolver as well as no hanging if connection breaks during download

This patch fixes the AssetsManager by ensuring that proper curl settings are done

AssetsManager (and the app using it) crashes if CURLOPT_NOSIGNAL is not set and there is a DNS resolution issue.  This is a known bug in curl on systems using posix threads and the recommended fix is applied here.

The AssetsManager perpetually waits if there is a connection timeout. The speed limit check enables curl to abort the download with a proper error code if there is a network connectivity issue.