Restore manual naming of static leases using comments for MKSCAN + cleanups

[kpolszewski]

reopen of #938

It was removed as part of #759 (exactly: https://github.com/jokob-sk/NetAlertX/pull/759/files#diff-3141c3ddff99ee9cccc877150d8bd75a6a5227c3f049d6fe7809ef27b77cbb71L91 ), however comments are used to provide custom device names for Mikrotik's static leases

I have:

• removed unused imports and unused "ips" param,
• created the device_name variable that tries to determine the name in order: comment>hostname>"(unknown)" fallback (so nslookup and other plugins can continue resolving from here)
• used all watchedValues that are defined in config.json

[jokob-sk]

Thanks @kpolszewski 💪 sorry for the confusion earlier

[jokob-sk]

Can you also update readme?