Minor Changes.
	- I have inserted a new table into the database called words. In this
	 table we are going to store relations between words and tweets. I
	 don't know if we are going to use it. But I think it will be helpful
	 and adding it later in the project will be a mess.
	- The databasecreator now is not case sensitive in word and hashtag
	 column.
	- The harvester now is more robust. The tweet insertion will only be
	 commited into the database if the whole tweet has been correctly
	 inserted.
	- Now the harvester source code is clearer to read. I have divided the
	 code into different functions.
	- Now the harvester inserts words to the database too.