Fix keyword search to save old tweets and all tweets between crawls

Introduction
=========
We have made improvements:
* Crawl save old tweets when you start a saved search, not only the last **tweet_count_per_call** tweets with maximum **archive_limit** tweets
* Crawl save all tweets between consecutive calls by saving since_id and max_id in database
* If there is an API call limit problem and searching tweets is interrupted, next time it will continue and you won't lose any tweet

Changes
=======
* New function getLastPostIDByHashtag in HashtagPostDAO interface
* Modifications in getLastPostIDByHashtag to ensure capturing all tweets from a search


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