handle properly long inactivity pauses and recieving duplicates

this resolves #30 & #46

inspired by https://github.com/jmandel/sevabot/commit/29f21c1430ef28511b20dbfd53a1fa1c04fb0469
also see: https://github.com/opensourcehacker/sevabot/issues/68 && https://github.com/bkmeneguello/sevabot/commit/f783e9849e1856ea812567f9eacc46b50f211a93

the problem is, that *after some time of inactivity* skype **won't** call "CHATMESSAGE 19017 STATUS RECEIVED" on incoming message ever, it calls **only** "CHAT #.../... ACTIVITY_TIMESTAMP 1403896553".
Thats how we are loosing messages. I consider that as skype bug.

besides of that, patch is handling messages, which are coming while bot is being restarted,
for details why HashMap & lastReceivedId weren't working see comment around ```bytes:```

I also insist, that this logic about deduplicating and missing messages querieng do belong to library, not application layer.

Anyway within one chat it's perfect for me.