QtIFW

Revert 4ad2fe4d4a4 in favour of a more generic solution.

Task-number: QTIFW-156
Task-number: QTIFW-157

When we disable both package manager and updater radio button,
we will never be able to add a valid repository anymore. Now
use a more generic implementation and print an error message
if we try to access the network without a valid repository.

Change-Id: I27e4a7db96695b8ca32f391f910e455a553cc73e
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>