Added contact sync v2

Ported from yowsup, replaces
https://sro.whatsapp.net/client/iphone/iq.php
Returns decoded JSON object, need to build a simple parser.
Updated contact sync v2

Added JSON parser, returns array of existing users.
Non-existing users are skipped.
Updated comments.
Updated contact sync v2

Updated field from lastseen to lastupdated
thanks to alist3r
https://github.com/alist3r/yowsup/wiki/Contact-Sync-V2-API-results-guide
Updated contacts sync v2

Changed constructor to accept single phonenumber as well as an array of
phonenumbers
Split login method

Added method to login directly using password. This will skip the
credentials check.
Merge pull request #315 from shirioko/master

Added contact sync v2