Refactor Qt Installer Framework to Better Match New Versatile Requirements

Current structure of Qt IFW is such that Installer UI and other IFW components are tightly integrated together. This makes modification of the installer UI really difficult and causes unnecessary restrictions to how Qt IFW can be used and also maintenance is difficult.

To make Qt IFW more maintainable and easily usable for different possible use cases we should restructure it so that framework is split into clear separate logical parts, Package management, repository management, network access, file management and user interfaces.