Add unfavorite edge processing in hashtag/url path

[guimingTang]

This is yet another follow up change set to add unfavorite edge indexing in GraphJet, this time we add this functionality for Hashtag/Urls. In the tweet counting algorithms, tweet, hashtag, and urls all share the same graph traversal logic, i.e. they all collect and index unfavorite edges. However, during candidate generation, tweet and hashtag/url have a separate code paths. We previously patched up the tweet code path, but neglected hashtag/urls. This request consolidates the unfavorite logic in one place, i.e. GeneratorHelper.java. Also added new tests to cover hashtag/urls.

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