Qbs: Fix memory leak in Qbs Project Manager

Make sure the root node of the project tree is actually deleted.

Change-Id: Idf32460d7b5d0518da9536084cccb074638cfce3
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
RunSettings: Do not needlessly recreate RunConfiguartionConfigWidgets

Change-Id: I0b8afe05b12123117959eec6f7465ebd4950e197
Reviewed-by: Daniel Teske <daniel.teske@digia.com>