Added Signal/Multithreading to Get Tweets

- Added signal catching to the get_tweet's program, on port 5554. Will successfully add new companies to the company list upon a user signal.
   - Incorporates multi-threading into the get_tweets program.
   - Still needs a clean way of killing the thread upon keyboard interrupt, will fix later.

- Added a function to tweetcache called, "addCompanies", that appends a company name to the self.companies list.