Created KeywordService trait and moved MongoKeywordService to a different file
Fixed problem with encoding in Main.scala
Created DummyKeywordService
Added an option to GuiceModule to use DummyKeywordService instead of the Mongo one
Added SimpleREPL, a main() with a simple REPL for testing the summarization
Created Summary object

Now instead of returning the JSON Summarizer returns a Summary object.

The Summary object is a Traversable[String], meaning you can iterate on
the sentences directly from it.
It also has two utilitiess: charCount lazy val and takeChars method. The
latter can be used to return a new Summary which obeys to the
limitCharCount passed as paremeter.
merged @felipehummel changes