Support for wrong login info/for logging out at end of session

The web scraper will now stop trying to execute once it realizes that
the login info it has been given is not valid. The web scraper now also
logs out at the end of its execution process, which is necessary because
session data and cookies are kept between app launches, which means
things will be messed up if the app starts, logs in, exits without
logging out, and then starts up again