Extract Keter UI into Euclid

[ForNeVeR]

Well, we obviously have some problems with this project. The main problem I see is the UI implementation: I'm too tired implementing my own MVVM framework in Scala.js in scope of Keter.

So, I suggest we revivify the development somehow. I'd like to extract the UI parts to external library (Euclid will be the name), and also port it to work in the standard OS terminal (with additional support for rot.js). That way, the project complexity induced by inventing our own UI library will be moved away, and we could focus on the main game parts instead.