adblock-fast: explicitly allowing domains for dnsmasq.servers

adblock-fast: explicitly allowing domains for dnsmasq.servers

New features:
* explicitly add allowed domains on download/allow to the dnsmasq.servers
  config file

Cleanup:
* remove unneeded EXTRA_COMMANDS
* remove unneeded EXTRA_HELP
* remove unnecessary `\n` escapes
* remove unnecessary line breaks from output on download

Optimization:
* simplify is_integer()
* replace long if with case
* more verbose output on download

Signed-off-by: Stan Grishin <redacted>