added first working implementations of install_pkgs and find_required
- add const for pkg installer and deps resolution
- use English
- use Modern::Perl
- basic sub check_privileges implemented
- now able to install packages (urpmex::Urpmex::install_pkgs)
- now able to check installation dependencies
  (urpmex::Urpmex::find_required)
- added checkbox to choose automatic/manual deps installation
- available radio button now selected by default