Combine actions.py and commands.py into interaction.py

Combine actions.py and commands.py into interaction.py

We're about to create a new slash command that fires up a modal, and
the response to that modal will be an action. So we want the
implementation of that slash command (which creates the view for the
modal) to be in the same file as the handler for the action.

So we combine these together for now.

If this file become unwieldy later, we can re-separate things based on
functional groups, (interactions related to hunts, puzzles, word-play
utilities, etc.), but always keeping the view creators and the
view-submission handlers together for any given view.