Package installer-alterator-pkg: Information

- write the amount of space needed to a file in bytes
- add the ability to select additional packages before partitioning the disks
  + write selected packages to a file and read them during installation
  + do not install packages after selecting
    if the disk is not already partitioned
  + mount virtual filesystem only before installing packages
- allow to go back one step if the disk is not partitioned yet

- initinstall.d/90-pkg.sh: fix mkdir /var/lib/install3 when run from not '/'

- add reading checkbox state from conf file