Put page->talk page logic in get_talk_page method

Added a method to handle getting the talk page for a page in a given
non-talk namespace.
Added main shield, moved user-agent to config file

Put the body of the program under `if __name__ == main:` for better modularity.
Moved the user-agent string to the matchbot_settings.py config file.
Cleaning up notes and comments
Sketched out some methods for cat matching/posting

Built skeleton methods for matching, posting greetings. They
need to be filled out; not sure about the category matching ones.