GH-16 new perl module Pam::Exec

- The script pam-exec-user.pl is designed to be run via pam_exec.so module
- Commands to be run can be defined with a config file "pam-exec.ini" in the ".config"
  directory within the users home.
- Module Pam::Exec should be installed system-wide.
- Enable via configuraion in "/etc/pam.d/"
GH-8 add perl5 module support to bootstrap.pl

- install all modules in perl5 directory that are not present on the system
- uses Dist::Zilla for building
- installs with cpanm
- for system-wide installation put "system_wide = 1" in "dist.ini"
GH-16 configure system-wide installation for Pam::Exec