Add API Endpoint for MoviePolls

[CptPie]

As discussed in MoviePolls#11 a API endpoint would be needed to determine a running movie (although just checking the response would also work)

[zorchenhimer]

At the very least, I'd like an API endpoint to return the current movie title (set by the /playing command).

Authentication should also probably be a thing, but configurable (open/no-auth vs API key).