Test: Add unit tests for SteamChatBot

Add unit tests for the SteamChatBot module. These tests are used to
validate the SteamChatBot.Connect() method for three use cases: when the
user provides a username and password and no sentry file exists; when
the user provides a username, password, and Steam Guard code and no
sentry file exists; and when the user provides a username and password
and a sentry file exists.