QtIFW

Fix deadlock in elevated Settings operation

There are cases where using the RemoteFileEngine through QSettings will
dead-lock. Avoid this by using QSettingsWrapper directly, like we
already do in the rest of the code.

Change-Id: I2e00e107c5ab471ddd6cd79fed96417bf4351c1e
Task-number: QTIFW-618
Reviewed-by: Niels Weber <niels.weber@theqtcompany.com>
Reviewed-by: Jarek Kobus <jaroslaw.kobus@theqtcompany.com>