Smarter answer validation 

#### What's this PR do?
Uses regex to be a little more flexible with validating correct answers. For example, we want to allow an answer of 'A)' or 'A.' even if our `valid_answers` array in the config file only has 'A'.

#### What are the relevant tickets?
Issue DS-174
Haha. For now, the app will just return the previous message if no correct response is received. Hopefully that'll be sufficient.