Added data filter to the BotAdversarialDialogueTeacher to remove repeating "Hey do you want to talk about something else" episodes.

[leox1v]

In the data ~7k episodes end with "Hey do you want to talk about something else". With this flag we can skip these episodes.

[jxmsML]

wonder if we could replace the flag with a "mutator"

[leox1v]

@jxmsML thanks for the comment! I changed the filter to a mutator. What do you think?