Simple keyword list

Add a simple, case-insensitive keyword list to search for in pastes. 

- Populate a text file with keywords/phrases to search, one per line. 
- These keywords will be searched for in pastes. If one or more keywords are found in a paste, a tweet will get posted with the number of keywords. Additionally, if you elect to use a storage backend (Mongo), the keywords will get saved with the paste. 
- The file can be configured in settings.py

This PR also adds a few things to the .gitignore, adds a pip requirements file, and fixes a small issue with logging.