Some interesting cleanups

PackageKitBackend: Port superfluous kTransform to QHash::values()

OdrsReviewsBackend: Remove superfluous noexcept from destructor

ResourcesProxyModel: Port unconventional list manipulation to filter-map approach

The new code still uses in-band signaling, so to speak, in a form of -1 default value, for the lack of better options in Qt API. But at least now it is localized within the predicate, and does not get inserted only to be subsequently removed from the list, potentially causing an extra allocation.