Re-writing the builder from scratch with Debian repos

- Division of parts of the script into different functions
- Adding a check to make sure that the script is being run with administrative privileges
- Adding an option for cleaning the build environment before starting new builds
- Implementing package caching for local builds.
   While doing the development, a lot of time is wasted for downloading
   the packages again and again during the build.
   This time could be saved by caching the downloaded packages using apt-cacher-ng