Better 401 handling

[mm-pagely]

Overview:

• add methods to GuzzleTrait to set/unset handler functions for specific http status codes
• catch 401 in the base API client and throw a LoginRequiredException
• add a command trait (LoginRequiredTrait) that extends Command->run() to check the user's status and ask them to log in if need be
• add extra input validation to the login command