0.18 version

[thotmx]

Thank for your enjoyable 13-steps tutorial in Cultivate HQ blog.

But it was a little difficult trying to upgrade the tutorial to version 0.18.

https://github.com/thotmx/seat_saver

Each part has one commit. From Part 11 to 13 there is another branch.

I hope it would be helpful to people trying to understand your tutorial with the new version. (As I mentioned, I'm a newcomer, so maybe some concepts that I understand are wrong :().