Implement basic features for formatter

The base functionality of the module is ready now and can already be reviewed, but I will keep this issue as "Needs work" right now since I will also write a proper README.md next.

Nice work! I added a few comments. 🙂

I only looked at the code yet and haven't manually tested the module in our dev environment. So once everything is resolved, I can start doing that! 👍

@lrwebks, was this ready for rereview again?

@grevil, the README is still missing, so I'll take care of that and then put the issue to “needs review”.

A last thing that should be done is to take into account different image styles for the local video poster image, so I will do that next before we can call this one done.

This is off to review again, and as far as I can see, done (implementation-wise)!

For final test and review by @thomas.frobieter! 🎉