Improve silent QNetworkSession management via QNetworkAccessManager (Symbian)

If an error, which terminates the open network connection, occurs during a HTTP request the QNAM uses device level default configuration and depending on device settings the connection query might be displayed.

Issues:
1. Application is not silent anymore
2. Application is blocked until the user responds to the query
3. User cannot be sure which connection is used, for example:
User wants to download files only via WLAN connection
OR
User is traveling in a foreign country and wants to connect only via public WLANs (e.g. FON / Wippies)
-> Default connection might be something else and cause major expenses.

Additional comments:
Current implementation of Qt connection management (either via external QNetworkSession or internal with QNAM) does not provide enough means to create reliable access point management logic. Connection management should be improved to overcome at least the above-mentioned issues. The desired configuration should be used either with external or internal QNetworkSession. QNAM::setConfiguration() does not guarantee that. For example, if an invalid configuration is set and external QNetworkSession is not open the QNAM uses its own internal logic to connect to the internet.