Automated setup

[friendly-bits]

Implements automated setup command, called when running sh /etc/init.d/adblock-lean setup or service adblock-lean setup:

• Make the script executable (if not executable yet)
• Create addnmount entry (if doesn't exist yet)
• Call gen_config() if config file doesn't exist yet, or if the user chooses to recreate the config
• If config file exists and the user chooses to keep it, call load_config() and upd_cron_job()
• Enable the service (if not enabled yet)
• Offer to install GNU utils if not installed yet (GNU awk, GNU sed, GNU sort)
• Offer to start adblock-lean

gen_config():

• New option cron_schedule (syntax: <cron_schedule_expression>|disable)
• Offer to create a cron job with default schedule

Action enable: call upd_cron_job().
Action disable: call rm_cron_job().
Action disable: call stop().

Detect and report 3 types of wrong URLs:

• 'github.com' URLs
• Hagezi dnsmasq-formatted URLs in the raw-domains URLs options
• Hagezi raw-domains URLs without the -onlydomains suffix

Updates README.md