Image Builder V2

There is an intention to upgrade the existing image builder system in order to add the following features:

* Allow customers to use their own unattended files with as fewer modifications as possible (ideally using one command only).
* Allow customers to extend post-install actions without modification core files. A folder structure will be created with predefined entry points.
* Improve support for multiple different platforms - create appropriate folder structure and logic to select and execute files from that structure.
* Make it more streamlined and flexible: 1) Avoid code duplicating; 2) Convert as much code as possible to functions and combine them into modules for reuse; 3) Reduce the amount of hard-coded values.