QtIFW

Make InstallerCalculator independent on PackageManagerCorePrivate

Inside PackageManagerCorePrivate:
- rename resetComponentsToUserCheckedState() into restoreCheckState()
- replace setCheckedState() with storeCheckState(),
complementary to restoreCheckState()
- call storeCheckState() before calculation of components to
install / uninstall

Change-Id: I8dde3be75a60ebac2fae5fcde1da1b609dd23256
Reviewed-by: Karsten Heimrich <karsten.heimrich@digia.com>